The following was previously published in an earlier edition of Marketing Insider.

As marketing gets more challenging and talent churn accelerates, agency selection takes on more urgency. The conventional approach — picking agencies for the moment in reaction to leadership or market changes — can put a company’s institutional knowledge and marketing rhythm at risk. Instead, marketers need an agency model that supports long-term, strategic planning and execution.

For most, that means either a full-service, single-source agency or an integrated agency team (IATs) of assembled specialist agencies. Both deliver results in the right fit. But they’re very different models with benefits and challenges. What’s the right agency model for your business?  Ask yourself these key questions early and often.

How complex is our challenge, really? The complexity of the marketing problem determines the jobs to be done and the depth of agency resources to develop the work. Do you need a new brand foundation, fresh creative, a different media mix, or a new way to win the intensifying retail environment? Eager marketers often want to take it all on, when it’s more useful to focus on what’s essential. Too many objectives and tactics overstretch internal and agency teams.

What do we have the resources for? IAT models provide depth of expertise, but come with high non-working agency costs. They also require considerable internal management expertise and time, including coordinating agency selection, contracts, workflow, invoice payments, annual reviews and more. It takes a sizable, collaborative leadership team to handle  IAT management and provide the ongoing direction needed to align creative output.

What kind of culture do we have? Is your organization more collegial or competitive? Agencies deliver the best results when the model matches the culture. If you have centralized leadership oriented toward long-term partners that act as confidants across functions (e.g., marketing, sales, product innovation), lean toward a single-source agency. If you have competing leaders with different goals and budgets, then cohesion comes best from an IAT. One agency will be more broadly strategic, while a portfolio of specialists will support a volume of initiatives.

With CMOs on a short leash and organizational resources in shorter supply, many marketers are leaning more heavily on agencies for both brainpower (insight, creative, analytics) and horsepower (hands to get more done quickly). How much momentum the client-agency relationship can generate depends largely on how the model matches the organization’s realities, not just an individual brand’s desires.

Will it be a full-service, single-source agency, or an integrated agency team of assembled specialist agencies? Here are some tips on how to decide.