it's probably almost unianimous that San Andreas and Vice City are the best 2
Vice city has the music, the cars, the clothes and the feel of the greatest decade
whereas San Andreas had the depth, the characters, the customisation and quite frinkly was longer, had more side quests such as horseshoe collecting, it had skill meters allowing you to feel the growth of CJ as you went on in the game with him, was more varied in it's locations, more varied in it's vehicles and to me, was not just the best GTA, but was one of the best games of all time