Joker's methodology is about playing games. A good mixture of subtlety and wanton acts. He even goes as far as assuming totally different identities and personas and actually embraces those roles. Some of whom even helped Batman until the game played out to the end.

Carnage is about mindless destruction. Sure he can disguise himself with his symbiote but he was too wild and destructive. I found Carnage's accomplices FAR more interesting than him. ie Shriek is awesome.

And Carnage was never funny to me or to the other comic book geeks I know. His name is Carnage, umm, okay? He loves to kill and write his own name in his own blood as a signature. Wow, he's a real genius. However, I did like him in his return recenetly. (5 part mini)