All are good games, but I think Vice City did the best job in terms of really making you feel like you were in the 80's. The music, the clothes, the neon. Plus Ray Liotta was the shit in that game. Storyline wise, it seemed to make more sense and it wasn't so all over the place like SA. However I love the size of SA, you can literally just drive around for hours exploring and still not see everything.
IMO Vice City>San Andreas>GTA 3