Tommy Vercetti. He's a genuine badass who really knows how to take charge, and if anybody crosses him, guaranteed, he'd end up plugging you like a duck. On top of that, he's a very snazzy dresser, and a sharp businessman. The guy ends up ruling Vice City with an iron fist at the end of his game, while all the others either go back to what they were before (Claude Speed, Toni Cipriani) or end up for the worse (Vincent Vance).
On a side note, I royally despise C.J., because he's the exact opposite of what Tommy is. Busta, busta, BUSTA in SPADES.