http://www.hollywoodreporter.com/bastard-machine/tim-goodman-colbert-should-replace-430383

It wouldn't be a youthful hire (Colbert turns 50 next year), but Tim Goodman says "Colbert could be the one host on the market who could combine the modernity of Letterman’s glory days with the genre-defining humor and panache of Carson while also tapping back into the seminal days of Dick Cavett/Jack Paar/Steve Allen."

http://tvhowl.com/2013/04/05/who-will-replace-letterman-enter-conan/

Conan is the most Letterman-like of the late-night hosts. Plus, he would give CBS a chance vs. the two Jimmies.