Well, Steve Allen, with his "Tonight Starring Steve Allen" invented the genre (1954-1957), what with the opening monologue, celebrity guest interviews, live band, etc. He was a riot, and very innovative.
But when Allen moved on, the great Jack Paar took over in 1957 to 1962, when he quit due to overwork. He was the best talk show host of all IMO. He had in-depth, intuitive, and humorous conversations with each guest, and made famous such entertainers as Jonathan Winters. He interviewed a wide variety of celebrities --not just movie people-- Like John F. Kennedy, William F. Buckley, and Alexander King.
But when Paar left, Johnny Carson took over, and he gradually became an institution over the next 30 years. I slowly grew to really like Carson. After Carson retired, I thought Leno and Letterman were okay, but they really didn't get much out of their guests. As far as the guys who came along after L & L, I wouldn't give you two cents for any of them.