I'll talk about the places I'm very familiar with:
Atlanta: I'm a Georgian, born and raised, incredibly familiar with the ATL area. Do not come down here without a car. Others have said the same thing in this thread, but I can not stress this enough. I've been on MARTA once and I won't do it again; the buses are atrocious. Even with the traffic, your life becomes much easier when you have access to a car.
re: traffic: in Forbes' list for worst traffic in the nation, we were #4. Just saying.
Nashville is similar, though smaller and with not as much traffic. I was ecstatic when I was finally able to take my car (I went to Vanderbilt for UG). You can't go to a grocery store without one (Harris Teeter and Kroger are the closest, but they are way beyond walking/biking range), so yeah. Also, I thought that Atlanta drivers were bad....Nashville drivers are horrible.