Atlanta for the win. Summers are hot and sticky but not unbearably long. Crime and traffic are big issues, but where you live can make a big difference for both. Chattahoochee river is fun. Stone Mountain, Zoo, Botanical Gardens, outdoor concerts at Chastain Park and Lakewood, and a museum dedicated to Coca Cola. Best part about Atlanta is that a lot of the suburban sprawl neighborhoods resisted the trend to clear cut and cram houses shoulder to shoulder (partly due to terrain and drainage, but also a conscious decision in many cases).
Dallas is a distant second. Summers are very long. 90s from May through October with several weeks of 100+ common in the middle of summer. Everyone at some point in time in Dallas has a vehicle damaged in a hail storm. Suburbs are soul sucking sprawl with no mature trees and houses jammed together like sardines. Downtown Dallas is a dump despite efforts to clean it up and make it more user friendly for people living in uptown. Only big plus is that a long day's drive will get you to the Rockies.
Phoenix is pretty dreadful and might become unlivable if global warming pushes temps up any higher in the summer. And water is going to be a big problem as the Colorado River is at record lows with no signs of recovering any time soon.
Miami gives Phoenix a run for its money. You have to pay a premium to make sure you have a home that meets Hurricane Andrew building standards. If you buy pre-Hurricane Andrew construction, you risk losing it all when Miami gets hit by the next big one. And you do have to evacuate whenever a hurricane targets Miami. That usually means spending 12-16 hours on the road to get to a hotel in GA or AL. Miami is full of tourist year round and lots of people pretending to be an international playboy.