Leaving out the clear 1-2 combination of Bremond and Cranfills Gap, I would have to say that I have really enjoyed the following for places to visit:
Chicago in early fall or late spring
Seattle in summer
San Diego just about any time
Washington DC in late spring
This is based on the city centers, with things to do, places to stay and eat, and likely weather. It only includes places I have been; there are plenty more places where I have not been that might be nice. I'm not sure how much I would want to live in any of these places, especially if I weren't earning several dozen boatloads of money.
The Poster Formerly Known as Maxwell's Silver Hammer