For late night I like Craig Ferguson.
Jimmy Fallon can actually be pretty funny. He did this thing where he sang a funny song mimicing a bunch of famous bands and her was really really awesome. He sang and played guitar. At least I think it was Jimmy Fallon, I heard it on SIRIUS. He is not very good on late night because he is seems like he isn't very sure of himself.
Good point... I also like Craig Ferguson.
Carson was "IT". He was naturally funny (an understatement), AND he could interview a guest better than anyone. Letterman, and Ferguson are also GREAT at interacting with guests. Leno has ALWAYS sucked at interviewing guests... so did O'Brien, and so does Fallon.
For example (Leno, or O'Brien, or Fallon interviewing an interesting guest with their script of prepared questions)
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Leno - So you had to do a same sex love scene in your latest movie. How did that go?
Guest - During the scene, I really enjoyed it, and frankly, I've now realized that I am more attracted to people of my same sex, and my co-star and I plan on getting married!
Leno - So you shot the film in New Zealand, what was that like?
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The guest drops a bombshell and Leno/O'Brien/Fallon can't see the opportunity to go off script. They don't have any ability to go into a spontaneous mode... I've seen this... IDIOTS!!!
Carson, Letterman, and Ferguson are comfortable to "go with it"... smoothly jump onto the bombshell and create some GREAT entertainment from it.
This ability by the way, is what put Carson head and shoulders above EVERYONE else... I've seen him keep a guest on for the ENTIRE show (bumping all others) because Carson realized he had something special going on with THIS guest, and he'd run and run and RUN with it for the entire show.