Big men's games aren't as designed for "clutchness", especially if they're not a very good free throw shooter. Go down low looking for that one bucket, and your big man is probably facing a double team while being hacked unrelentlessly by players trying to knock the ball out of his hands. Since it's the last play of the game, the refs are afraid to blow the whistle, and even if they do, you've got a 70% free throw shooter going to the line if he's good at free throw shooting for a big man. The proper play for someone like Howard is to draw the double team and pass to the open shooter, and not try to take the hero shot. So I cut him slack. It's not that he's not clutch, it's just that if you need one possession, you want to go elsewhere. If teams try that defense the entire game, they generally fail, but in the last 10 seconds, it works. (Dirk is an exception, because he's a great shooter who happens to also be big. KG is in between Dirk and Dwight, since he has some range, but not Dirk's range.)
I'd probably pick Carmelo if I had to pick anyone. He makes them occasionally, but I'm generally not scared when the Knicks have the last shot and he has the ball in his hands. I'm more scared of Smith.