Why does The Joker seem cooler then The Batman?

"I'm an agent of chaos."-The Joker

What this actually means is 'Haha!  You can't locate my motives.'  But if he didn't have a motive then he wouldn't be there so he isn't even an agent of chaos as he so claims.

"Kill you, I don't want to kill you, who would I be without you?  You complete me."

Damn right Batman completes him because The Joker is the main character in the movie The Dark Knight although it seems to be Batman.