I think all the characters are good
you've got something for everyone in there.
You've got Franklin for your nostalgia like Vegetunks says, 'going back to grove street', in my opinion i still think San Andreas was one of their best and i'm looking forward to revisiting that part of grand theft auto.
You've got Michael as your new story, i think the game is going to be pretty central around him. you'll probably do a few more 'serious' missions with him.
then you've got Trevor, as msbhvn says the 'comic relief', which is what was definetly missing from the last game, looking forward to some crazy ass missions with him
overall this looks sweeeeeet!