My favorite is III with VC literally right behind it. III was just super gritty and I played it for hours. I know VC is the better game but I dig III mostly for it being the first major one I played.
Call me old fashioned but GTA: London is my favorite. I would like a remake of that somehow over Vice City but obviously it is highly unlikely to happen.
I haven't played V (or I and II), but out of the rest, I would say San Andreas. I liked the way they had three cities, and country towns as well. They really tried to make it a game world. After San Andreas, GTAIV is my next favorite.So, which one is the best ever made?