Thirding Atlanta. My point of reference is Philadelphia (not in the bible-belt). Atlanta has significantly more startups and acquisitions than in Philadelphia, at least in the areas that I interact. Even with Philadelphia being home of First Round Capital, there isn't a lot of hometown investments in their portfolio compared to their SF ones.
This bashing of the 'bible-belt' is just silly. It's just as close minded and prejudiced as what the bashers accuse the residents of the 'bible-belt' to be. Go out to Western PA or northern New York and tell me about the 'startup culture' there vs. the bible-belt.
My guess is that nearly any metro area is going to have a superior startup culture compared with nearly any rural area. As far as comparing city vs. city, I would guess there isn't a real solid rule to follow. Probably requires some investigation and also factor in your own personal likes and dislikes.