TOD:
Of the current roster of late night "chat" shows, I only find Craig Ferguson worthy of a look. Otherwise, there's no one really that interesting or capable of interviewing people.
Ellen doesn't qualify because she is an afternoon show and the time-slot has a totally different audience. If she were a night-time chat show, I would place her in the same bracket as Arsenio, not Carson.
Merv Griffin, as deep in the closet as he was, always seemed to be chatty, catty and gossipy. I always looked forward to Orson Welles and his appearances on the program. I remember that on one occasion, Orson told Merv that it was never considered manly in the early 1900s to wear a wristwatch. The bending of the wrist to look at the watch was, according to Orson, where the stereotype of the limp wrist originated. The only acceptable watch a "man" could "wear" was a pocket watch. I will never forget the dagger eyes that Merv shot at Orson and then tried to shrug it all off with a nervous titter. But, Merv's show was must-watch TV.
Merv's show was the very first TV show that I ever saw John Williams. I don't know if he had been on TV, but that's where I first saw him as an interviewee. Around that same time, 1977, Andre Previn was hosting a PBS series called "Previn and The Pittsburgh" in which he and the Pittsburgh Symphony would showcase various golden and silver age movie music. The series was great fun for me. Many years later I read that many in the music community did not like Previn's show because he was "too opinionated". I liked the show nonetheless and learned a great deal about many of the great composers for film, some of whom were still alive and appeared on Previn's show.