NYC/Liberty City is my favorite but it's too soon to revisit. Miami again would be first choice. I don;t see why they can't go back to the 80's again where the coke and crime was so prevalent.
Modern London could be awesome as well if it played out like an early Guy Ritchie movie. --- Glorious God Gamers > PC Master Race > Console Peasants ---> http://i2.kym-cdn.com/photos/images/original/000/508/644/9eb.jpg
I wouldn't mind seeing their version of England again like in the original GTA. But any europeon city I. General would be neat.
R* already said it was an American game. They aren't leaving the country. The whole point is that it satirizes AMERICA. GTA isn't the same as it was with those first two games so don't say "It started as a British game."
Dan Houser said it himself: "but my own personal feeling is that GTA is America."