Well my favorite rockstar games are Red Dead Redemption and Bully. I haven't played San Andreas in years, but I'm going to buy it off XBOX Live and play it so maybe I'll be able to get a better opinion of that game.
San Andreas for me. Vice City was really really good, but SA just took that even further. I never really got into GTA IV. Red Dead is decent enough for the half hour or so that I watched it being played, but not good enough to be better than SA.
I hate how everyone jumps on San Andreas' dick. The game was not that good, just massive. More does not mean better, whereas you have games like Red Dead Redemption and GTA 4 that have obviously have such massive attention to detail in every single aspect of the game that, to be honest, it is ridiculous that they could pull it off.
Absolutely adored the game. Such a brilliant game limited only by current technology and how far gaming had progressed game-engine-wise.
GTA: San Andreas
Had some of the most fun on any game ever here. Its only even slight problem was its lack of identity but that's just because it tried to include so much craziness in one game!
Another brilliant game. The first GTA to really nail the narrative feel. The stripped out features were a shame but in the end it was just meant to be a different game. I loved the different direction personally -it's fantastic to see so many different secrets and so much exploration to be done in such a small world.
Bully Very different than the above; as much as people may call it 'GTA in school'. It was really fun; and even little mini-games like classes were fun rather than tedious. Was cool to somewhat experience American High School (even if it was in an extremely exaggerated way).
Red Dead Redemption Combined the brilliant narrative of IV with the extensive exploration in SA. Everything in the game felt so alive - amazingly immersive
L.A Noir Least favourite of all these but still a great game. Little repetitive.
Picked San Andreas but having second thoughts. Not sure, I loved SA/IV/RDR fairly equally so it's hard to decide.
To answer the question though, honestly can't pick. I loved SA and also Bully! Loved L.A Noire but not as much as those two. I have RDR at home somewhere waiting to be played. Should probably start that...