I’ll second the Powerpuff Girls vote. Letterman and Leno are getting too old, the entire genre is ancient and should be put to death humanely. Carson was smart to quit when the thrill was out of it.
Letterman. Especially when Richard Simmons is on. Bahahhhah!
Then I like Leno better when he has kids on the show.
But the overall ass-kicker in my book is, without a doubt, Conan.