GTA III is still my favorite one. San Andreas was alright, but I liked the feel of Liberty City more, and I liked the fact that it was less realistic. Cars handled way more arcade style, the city was set up a lot simpler, everything was a lot less like reality, and more suited for a videogame.
San Andreas did seem really hard, and I wasn't too impressed with the mood of the game. It all seemed so run down and polluted, once again, too much like a real city. :lol