Lead Generation Exclusive: Sole Or Multi Agency?

It's the question facing most advertisers. Should I place my budget with a single marketing agency who broadly speaking cover all the bases or should I identify performance marketing specialists and get them to work together? Performance marketing covers everything from affiliate, email, display, social, search and mobile marketing.
I don't think there's an answer to cover all situations in reality. But one thing does stand out, you should NEVER pick multiple agency's to do the SAME job. I have experienced this at first hand and whilst an inconvenient truce can exist for a while it is only a matter of time before one agency blames the other and looks to the client to referee the ensuing bun fight. At the end of the day, clients are only interested in results and do not want to be dragged into inter-agency issues. However, agencies are not the most self-regulating of creatures and instead clear terms of engagement need to be set down from the beginning. This is exactly what procurement departments can be brilliant at doing - designing a framework where multiple agency can work together to achieve perfect marketing harmony. Each lead generation channel should be given to the agency most capable of getting results. After all, if one agency was so great at everything then clients would be more than happy to put all their eggs in one basket. But I doubt this approach will ever triumph despite the ambitions of large agencies such as OMD & Carat, networks such as Unanimis & Tradedoubler or uber-platforms such as Google, Facebook or Twitter.
In an increasingly fragmented and uncertain world, the way to bring certainty is to harness the power of specialist agencies to work together for the common goal of exceeding client expectations, bringing innovation and ensuring clients receive more than a pound for every pound spent.