TOD:
I liked Johnny Carson, although I only watched on the rare occasion when he had a guest that was of interest.
Have not watched any of the other current talk show hosts enough to have much of an opinion, although I have seen each of them on other shows. Conan O'Brian always seemed creepy to me. David Letterman, I just never cared for.
If I had to pick a favorite talk show host it would be Ellen DeGeneres. I have seen her show only a few times, but it was always fun.