I have to say GTA Vice City was my fav so far, it has the nostalgia factor for me I love the Miami Vice theme it had, and the music was great. I haven't played GTA 4 yet, but I hear its awesome. Didn't care much for San Andreas
I dunno about most people, but I just cant identify with the plot of San Andreas, or the characters. THey're so.. lifeless. No laughter, no character... just sorta there. CJ's mom died, he's back. So what? Uniting the ghetto? I drive thru it, I try not to live there. Smells strange during midday.
GTA4? I can relate to all the characters with all their dialogue. They actually have stories to tell.