Vice City is the best for me. The story, the setting, the music, and Tommy Vercetti is easily the best GTA protagonist so far. San Andreas was great fun too, but i hated the whole Sims aspect of it, having to eat, go to the gym, pick up your girlfriend etc. It just got really annoying. III was obviously brilliant at the time, but there's no way i'd go back and replay it after playing VC and SA. It's very limited in comparison. IV...i got bored of IV pretty quickly, it looked nice and everything, but they took away the craziness that made GTA great. If they can combine the atmosphere and feel of VC, with the over the top craziness of SA, and the size and modern graphics of IV, then they could potentially have the greatest game of all time on their hands.