Max,

I guess what you really need to do is talk to them all, in depth, and find out how they work.

I am sure the work you need doing, you have already created a "vision" for in your head, and you need to find a person who can create your vision.

There are thousands of great designers out there, with impressive portfolios, but i know that a lot of these big companies dont work with clients, they just create something "they" like, and hope the client is happy, however their ability to "create" something that isnt in their usual "style" is what usually becomes the problem.

I think your best bet is finding a company that isnt "huge"... Maybe a team of 1 or 2 guys, and find out if they will work closely with you to create your vision, not theirs.