GTA's San Andreas is the all time good game. The intelligent small missions makes it unique compared to the other versions like Vice city or China wars.
I love to play vice city. To complete the various mission is very interesting. To select a car and drive it which enjoy me a lot. It's graphics is very cool.
I really enjoyed GTA IV out of all them. Not because it's the newest, but because the graphics were best, and the story was very strong.
San Andreas was the best one. It just seemed so easy to play, then GTA 4 made too many radical changes, that it became more of a chore to play, and I never made it that far into the story tbh, and some of the achievements made the whole "free roaming" seem more restriced since you had to finish the story line within a set time limit