Media Agencies: How to Choose the Right One for Your Business

Media agencies plan and buy advertising across channels on behalf of brands, but the differences between them, in terms of size, specialism, commercial model, and cultural fit, are significant enough to make the wrong choice genuinely costly. The top 10 media agencies by billings are dominated by the holding group networks: GroupM shops (Mindshare, Wavemaker, EssenceMediacom), Publicis (Starcom, Zenith), IPG Mediabrands (Initiative, UM), Dentsu (Carat, iProspect), and Havas Media. Independent challengers like Jellyfish and Assembly round out the picture for brands looking outside the holding company model.

Knowing their names is the easy part. Knowing which one is right for your business, and why, is where most procurement processes fall short.

If you’re thinking about media agency selection as part of a broader go-to-market or growth strategy review, the Go-To-Market & Growth Strategy hub covers the wider commercial context that should inform that decision.

What Are the Top 10 Media Agencies by Global Billings?

By global media billings, the landscape is dominated by a small number of holding group-owned networks. These are the agencies that consistently appear at the top of the RECMA rankings and COMvergence reports:

GroupM agencies: WPP’s media investment group is the largest in the world by billings. Its three main agencies are Mindshare, known for integrated planning and innovation; Wavemaker, which positions itself around positive provocation and commerce; and EssenceMediacom, formed from the 2023 merger of Essence and MediaCom, combining data and technology capability with traditional media scale.

Publicis Media agencies: Starcom has long been associated with audience understanding and entertainment marketing. Zenith, which coined the “ROI Agency” positioning years ago, has leaned into performance and data-driven planning. Both sit within Publicis Groupe, which has made significant investment in its data and technology infrastructure through Epsilon and Publicis Sapient.

IPG Mediabrands agencies: Initiative and UM (Universal McCann) are the two main media brands within Interpublic Group. Initiative has repositioned in recent years around cultural velocity, the idea that brands that move with culture grow faster. UM has a strong reputation in entertainment and sports.

Dentsu agencies: Carat and iProspect are the flagship media brands within Dentsu. Carat is one of the oldest independent media agency brands still operating and has a strong planning heritage. iProspect started as a pure performance agency and has evolved into a full-service digital media network. I spent several years inside iProspect during a period of significant growth, and I have a clear-eyed view of both what those agencies do well and where the holding group model creates friction.

Havas Media: Havas operates a “village” model, integrating media, creative, and PR under one roof in many markets. It has a strong presence in Europe and has positioned itself around meaningful brands, arguing that brands with genuine purpose outperform over time.

Independents: Jellyfish (now part of Brandtech Group) and Assembly (part of Stagwell) represent the challenger tier. They attract brands that want more senior attention, more transparent commercial models, and less exposure to holding group trading arrangements.

How Do Holding Group Media Agencies Actually Make Money?

This is the question most pitch processes never ask directly, and it’s the most commercially important one on the table.

Holding group media agencies make money in several ways: management fees or retainers paid by clients, volume bonuses and rebates from media owners based on total group spend, proprietary trading desk margins (where the agency buys inventory at one price and sells it to clients at another), and data licensing arrangements. The mix varies by agency and by market, but the structural reality is that the agency’s financial incentives are not always perfectly aligned with the client’s media objectives.

This is not a scandal. It is a business model. But brands that don’t understand it going in will find themselves in contract renegotiations they weren’t prepared for. When I was running an agency, the conversations that were hardest to have with clients were the ones where they’d signed a contract without understanding the difference between gross and net billings, or hadn’t asked about principal trading arrangements at all. Those conversations happened because procurement had focused on rate cards rather than commercial structure.

The ANA in the US and ISBA in the UK have both published reports on media transparency that are worth reading before any agency selection process. They document the gap between what agencies disclose and what actually happens in the trading chain. This isn’t about distrust, it’s about informed commercial decision-making.

Independent agencies tend to operate on simpler commercial models, typically a transparent fee plus a percentage of spend, with no proprietary trading. That clarity has commercial value, even if the rate card looks higher at first glance.

What’s the Difference Between a Media Agency and a Media Buying Agency?

The terminology has blurred over the past decade, but the distinction still matters in practice.

A media buying agency, in the traditional sense, executes the placement of advertising across channels: negotiating rates, booking spots, managing schedules, and reconciling invoices. It is an operational function. A full-service media agency does all of that and also provides strategic planning: audience analysis, channel selection, budget allocation across the funnel, measurement frameworks, and increasingly, data and technology consulting.

Most of the top 10 agencies position themselves as the latter, but the reality of what a specific client team delivers depends heavily on the size of the account and the seniority of the people assigned to it. A £2 million account at EssenceMediacom is not getting the same strategic resource as a £50 million account. That’s not a criticism, it’s arithmetic.

The agencies that have genuinely invested in planning capability, as distinct from buying scale, tend to be the ones with strong proprietary research tools, dedicated strategy functions, and senior planners who stay with accounts rather than rotating through them. Asking to meet the actual team, not the pitch team, is the single most useful thing you can do before signing a contract.

How Do You Evaluate a Media Agency Beyond the Pitch Deck?

Pitch decks are marketing documents. They are designed to win business, not to give you an accurate picture of day-to-day service. I have sat on both sides of that table enough times to know that the agency that wins the pitch is not always the agency that delivers the best work.

There are five questions that cut through the theatre:

Who will actually work on my account? Not the pitch team. The actual account team. Ask for names, titles, and how many other accounts each person manages. A senior strategist managing 12 accounts is not managing any of them well.

How does the agency make money from my account specifically? Not in general terms. On your specific contract. Ask about management fees, trading arrangements, data licensing, and what happens to volume bonuses attributable to your spend.

What does the agency’s measurement framework look like, and who owns the data? This is increasingly critical. If the agency owns your audience data, your attribution models, and your campaign history, switching agencies becomes significantly more painful and expensive. Data portability should be a contractual requirement, not an afterthought.

What does the agency recommend you stop spending on? Any agency that only tells you where to spend more is not giving you a strategic view. The best planning conversations I’ve had with clients involved recommending significant reductions in channels that looked productive on last-click attribution but weren’t driving incremental growth. That kind of honesty is rare in a pitch, but it’s what good planning actually looks like.

Can you speak to a client of similar size and category who has been with the agency for more than three years? Not a reference the agency selects. A reference you find independently. Long-term client retention is the most honest signal of service quality in this industry.

Understanding how media investment connects to growth strategy more broadly is something I explore in depth across the Go-To-Market & Growth Strategy section of this site.

What Do the Best Media Agencies Do That Others Don’t?

The agencies that consistently produce better outcomes for clients share a few characteristics that don’t show up in credential decks.

They treat reach as a strategic variable, not just a media metric. Earlier in my career, I overvalued lower-funnel performance channels because the attribution looked clean. The numbers made sense on a spreadsheet. What took me longer to understand was that a significant portion of what those channels were “converting” was demand that already existed, people who would have bought anyway. Real growth comes from reaching people who don’t yet know they need you. The media agencies that understand this distinction plan differently. They allocate budget to build future demand, not just capture current intent. The ones that don’t are, in effect, helping you harvest a field you’ve already planted.

They are honest about what measurement can and cannot tell you. Attribution models are useful approximations, not ground truth. The best planning teams I’ve worked with are comfortable saying “we think this is working, and here’s why, but we can’t prove it with the precision the CFO wants.” That intellectual honesty leads to better decisions than false precision does. For context on how growth strategy and market penetration interact with media planning, Semrush’s overview of market penetration strategy is a useful starting point.

They push back. The agencies that add the most value are the ones willing to tell a client that their brief is wrong, their budget is misallocated, or their expectations are unrealistic. That requires a relationship with enough trust and commercial security to have an honest conversation. It also requires senior people on the account who have the confidence to say difficult things. Junior teams optimise for client satisfaction scores. Senior teams optimise for client outcomes. The two are not always the same thing.

They think about the whole funnel, not just the bottom of it. Go-to-market execution has become genuinely more complex, and media agencies that can connect upper-funnel brand investment to downstream commercial outcomes are significantly more valuable than those that treat brand and performance as separate conversations. The best agencies have stopped pretending that division makes sense.

Should You Use a Specialist or a Full-Service Media Agency?

The case for a specialist agency, one focused on a single channel like paid search, programmatic, or social, is strongest when you have a mature media strategy and need deep technical execution in a specific area. If you’re spending £5 million on paid search and you know that’s the right channel, a specialist agency with genuine technical depth in that channel will likely outperform a generalist team at a larger network.

The case for a full-service media agency is strongest when you need strategic planning across channels, when your budget allocation is still being determined, or when you don’t have the internal resource to manage multiple agency relationships simultaneously. Coordination costs are real. Having four specialist agencies that don’t talk to each other creates gaps, overlaps, and attribution disputes that consume internal bandwidth.

The hybrid model, a full-service agency for strategy and planning with specialist execution partners for specific channels, works well in theory but requires a client-side lead with the commercial and technical confidence to manage it. Without that, it tends to collapse into either the full-service agency absorbing everything (often at lower quality than a specialist) or the specialists operating in silos.

Category matters too. A pharmaceutical brand handling regulatory constraints in media placement has different requirements than a DTC fashion brand optimising for cost per acquisition. Forrester’s work on go-to-market challenges in regulated categories illustrates how category-specific constraints should shape agency selection criteria.

What Does the Holding Group Model Mean for Mid-Sized Brands?

The holding group media networks were built to serve large global advertisers. Their scale, their trading relationships, their technology platforms, and their organisational structures are optimised for accounts spending tens or hundreds of millions annually across multiple markets.

If you’re a mid-sized brand spending £3 to £15 million in a single market, you are not the client these agencies were designed for. That doesn’t mean you can’t get good work from them, but it does mean you need to be realistic about where you sit in their commercial priorities. When I was growing an agency from 20 to 100 people, the accounts that got the best service were the ones that were commercially important to us, not necessarily the biggest names on the roster. A £1.5 million account that was growing fast and had an engaged client team got more senior attention than a £4 million account that was flat and adversarial. Agencies are run by people. People respond to relationships and momentum.

For mid-sized brands, the independent agency market is worth taking seriously. The commercial models are often more transparent, the senior team is more accessible, and the agency’s incentive to retain your business is proportionally higher. BCG’s thinking on brand strategy and go-to-market alignment is relevant here: the agencies that can connect media investment to brand strategy tend to deliver more durable commercial value.

How Is the Media Agency Landscape Changing?

Three structural shifts are reshaping what media agencies do and how they compete.

First, the growth of retail media networks, Amazon, Tesco, Boots, Walmart, and others, is creating a new category of media inventory that sits closer to the point of purchase than traditional media. Agencies that have built capability in retail media are better positioned to help brands capture demand at the moment of decision. Those that haven’t are scrambling to build it.

Second, the deprecation of third-party cookies and the tightening of data privacy regulation is forcing agencies to rethink how they plan and target audiences. First-party data strategies, contextual targeting, and attention-based measurement are all gaining ground as alternatives to the cookie-dependent models that dominated programmatic buying for a decade. The agencies investing in these capabilities now will have a structural advantage in the next phase of digital media.

Third, AI is changing the economics of media operations. Bid management, creative testing, audience segmentation, and reporting are all being automated at a pace that is reducing the labour cost of execution. That’s good for clients in theory, but it also means agencies need to find new ways to demonstrate value beyond operational efficiency. The agencies that will matter in five years are the ones that can offer genuine strategic thinking, not just faster execution of the same tasks.

For brands thinking about where media investment fits within a broader growth strategy, the Go-To-Market & Growth Strategy hub covers the commercial frameworks that should sit above any channel or agency decision. Media is a tool. Strategy is what determines whether that tool is pointed in the right direction.

What Should You Actually Ask for in a Media Agency Brief?

Most agency briefs are too focused on deliverables and not focused enough on the commercial problem the brand is trying to solve. A brief that says “we want to increase brand awareness among 25-44 year olds” is not a brief. It’s a channel objective dressed up as a business objective.

A useful brief answers four questions: What is the commercial problem we are trying to solve? What does success look like in terms the CFO would recognise? What do we know about how our customers make decisions, and where media can influence that process? What constraints (budget, regulatory, competitive) should the agency plan around?

Agencies that respond to a brief like this with a genuine strategic answer, rather than a channel plan dressed up as strategy, are the ones worth talking to further. The ones that lead with reach and frequency numbers without connecting them to commercial outcomes are showing you exactly how they think. That’s useful information.

I’ve seen briefs that ran to 40 pages and produced mediocre responses, and one-page briefs that generated genuinely sharp strategic thinking. The quality of the brief signals to the agency how commercially sophisticated the client is. Agencies calibrate their response accordingly. Write a sharp brief and you’ll see who can match it.

For brands exploring how media agency selection connects to broader growth and acquisition strategy, Semrush’s examples of growth strategy in practice and CrazyEgg’s overview of growth approaches offer useful context on how media sits within a wider commercial growth model.

About the Author

Keith Lacy is a marketing strategist and former agency CEO with 20+ years of experience across agency leadership, performance marketing, and commercial strategy. He writes The Marketing Juice to cut through the noise and share what works.

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