The idea of a birth mother racing with the daughter she gave up for adoption is appealing, I don't see them being able to work well together in the long run. Admitedly, the problems they had this leg had to do with other things (like not really knowing how to drive a stick shift well) but I just can't see them lasting long. I also suspect that the tattooed couple won't last long since they aren't exactly the brightest people around. I'd kind of like them to stay for the comic relief, e.g. trying to get the flag from the "battle man" instead of taking it from the "battlement" and replying "uh, London?" when Phil asked them what country they were in.
So who do I like? The Princeton guys have an appealing sense of humor. The doctors seem pretty competent and could do well. (But what is with the blond one testing her blood sugar while driving? And isn't 337 an awfully high number?) The Asian father and son coud be interesting, too. I'm less sure about the father and daughter team, which is probably my bias about his backwoods accent.