In terms of the most entertaining character it is Trevor for me. What he does when you switch to him, what he says and nearly every cut scene he is in is pure comedy gold.
I like Michael but not all the time and Franklin is a little too straight up. Both Trevor and Michael make him look like a boy scout. Well I guess he has to learn from someone, I just wish he would cut loose a bit more and go wild.
All this is in the context of a computer game and that game being GTA. In all the GTA's I have always done chaotic things just to see how far I can make it against the cops after me.
As far as knowing someone like these characters I would rather have a mate like Franklin because Trevor is too out there and you can't trust or rely on Michael.