Choosing a digital agency to work with can be difficult. The most important thing to consider is the type of relationship you are looking for. In general agencies fall into two categories: partners and venders. Neither is better than the other. However, they have key differences that can break or make the relationship.
"The first step in choosing the right digital agency is deciding what kind of relationship you’re looking for." http://www.farreachinc.com/blog/far-reach/2015/12/02/partner-vs.-vendor-how-to-choose-the-right-digital-agency