I changed OBs after I had the birth classes and a tour of the hospital. I heard some comments here and there that scared me about the previous OB. The instructor of one of the birth classes talked about a water birth and I had always wanted to do that but didn't know of a local practice who did them UNTIL I talked with the instructor.
When I switched to the OB & midwife practice, I did not delve into my history. They were more concerned about me having a healthy pregnancy and a healthy delivery.
Fast forward - I ended up being induced because I was two weeks late. Every "natural" method to induce earlier didn't work.
Other than being two weeks late, everything went well. No complications.
I did not see my OB at all the entire time. I think I met him for the first time after I gave birth. He turned out to be one of the nicest people I've ever met.
Do you want to work with an OB where you have to prove your case? Wouldn't you want to work with people who were CONFIDENT that they could provide you with excellent care?
My understanding with the midwives is that they'll call on the OB if they run into complications. If they are already nervous about working with you, they may call in the OB earlier than they typically would and then the OB might act sooner than she might normally would (i.e. do a C-section before it's necessary).