Most people would agree that these 2 are among the very best of the GTA series and my 2 personal favourites. I recently purchased both of them for my iPad 2 and gotta say they're still as fun as ever.
Vice City just pips it for me cuz of the atmospheric location (I wanna go to Florida ) and the fact that it's set in the 80's which means CHEESY MUSIC. The storyline was really sweet too.
San Andreas was great too. Huge map, west coast location and music etc.
WBU?