I think a year from now the rating 1-2-3 will be Letterman/Kimmel/Conan. Conan doesn't have a chance for 2 reasons: the awful NBC primetime lead-in (and I've noticed CBS is running more Dave promos in prime time to take advantage). Second, he's handicapped by frequently having as guests the stars of those NBC shows no one watches. Yes, Carson still stayed on top when NBC was third for a while, but I don't recall Johnny ever having the cast from Supertrain or Pink Lady on his show. Also, Conan is no Carson....unfunny, nervous, overly scripted, tries wayyy too hard and it shows...a lot of flop sweat on that show.
Kimmel would be the funniest of the 3 if he stops all the Uncle Frank and Beatrice skits...always unfunny. Cousin Sal on the other hand, hilarious.