Alright.. Grand Theft Auto: Vice City.
Had an AMAZING soundtrack, the lineup of songs they had for the radio stations was phenomenal. I loved the setting that it was in, got me quite involved in 80's culture with all the references to Miami Vice.
Grand Theft Auto: San Andreas.
I still play San Andreas regularly, the story was amazing and a breath of fresh air for the franchise in regards to the setting, focusing mainly on a street gang on the streets of essentially Los Angeles instead of the mob (atleast in the early parts of the game). The addition of the San Andreas Multiplayer mod, which I personally love has kept the game popular for quite some time after its release. There's a definite case for it being the best GTA of all time.
Grand Theft Auto V.
The biggest Grand Theft Auto of all time, I loved it. I remember first getting that game Year 8 and I'd play it constantly and then go to school and talk about it all day with friends, absolutely killer graphics and the contrasting stories of the three main characters was interesting to me. Although, the overall story wasn't AMAZING, it was still a decent game.
Also a big fan of the Vice City Stories game, wasn't the biggest fan of Liberty City so those aren't that interesting to me.