After being in rescue, my first step would visit local rescues and tell them you're in need of a vet. They will know all the vets in the area and have heard all the good and bad about them. I'd listen to which one they use. Mostly, if a vet is sympathetic enough to work with a rescue, then you know they are in it for the love of animals and not the money their owners spend.

Outside that, I want one who will
A) listen to my thoughts, and trust my instincts. If I say my pet is sick, and they find no reason this pet is sick... LISTEN to me! I KNOW my pet and I KNOW when they aren't feeling well. This is VERY important to me and a lot of vets I've run into DON'T do this
B) Respect me. I am intelligent. Don't talk down to me.
C) Respect my pet. They are people too
D) Be honest with me.
E) Call me personally to give me results of any tests. NOT have the techs call me. I find that insulting and a waste of time because I usually ask more questions where the poor tech has to find out the answers, then call me back. Only for me to ask more questions where I'll need them to call me back again.
F) Have courteous and polite (aren't they one in the same?) vet techs and receptionists.

Thats all above and beyond the basic of having appointments available and such.