Trevor and Michael are more charismatic than Franklin, but Franklin is the only one that the gamer is likely to be able to enjoy as a "fantasy" avatar. He can at least seem somewhat normal and fun to play.
Redneck Psycho and West Coast Tony Soprano are both pretty off-putting and pathetic, though they're very well acted.
I gave Franklin the nod because I enjoyed living it up with Chop in that fancy house up in the hills.
The best GTA protagonist of the generation... was not a GTA protagonist.
Wei Shen. Great fashion sense. A genuinely appealing character, unlike the various losers and maniacs of recent GTA games.