Hey Diana,
What is a "comprehensive full stack of web dev as a service" that you're looking for -- like what would you need to get developed? Is stuff for Marketo or more like a website outside of Marketo?
Most of the agencies you've listed here I've seen in one-form-or-another turn out full-stack solutions, chances are pretty good that someone in the mix there can help you to accomplish what you're after (if it has anything to do with Marketo). A lot of times there's a "run of the mill" (normal) setup and structure for Marketo projects that the sales teams are more aware/aligned with but I'd imagine any one of the companies you've listed above could help get most things into play and a few of them could probably do-it-all.
What you really want to be looking for here (in my opinion) is:
1) Depth of Marketo expertise - there are tons of full-stack developers out there but making sure they are fluent with Marketo can make all the difference.
2) Short-term cost vs. Lifetime value - there are also tons of developers that can get a custom solution into play that trend from cheaper to expensive in costs and short-term to long-term in terms of solvency. Instead of looking at the short-term (up-front) cost of a complex project it might also be helpful to view it in terms of the lifetime value of the solution. I've personally come across many situations where we're asked to fix something that was either done in a hurry or on a budget and is now creating a problem instead of a solution. For this reason, I really recommend getting a good feel for the depth of an agency's work and knowledge base before considering the dollars and cents of it.
3) It is always helpful to have a clear idea of your expected outcomes and requirements to talk thru with an agency and see about what is/is-not possible within the context of Marketo -- most things should be possible in one way or another for an experienced team.
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