Conan is in HD. CF and the Colbert are not...hence the reason why I keep to Conan. I think Conan maintains to be funny but hey, different strokes for different folks. That's my kind of comedy - and similar to my line of jokes in real-life!
The killer part takes place during the interviews. Jay Leno, Letterman, CF - everybody else is truly a bore during the interviews with guests. Conan, however, remains a clown and continues to deliver laughs upon laughs. That's why you never get bored of him whereas Jay Leno (among the other subordinate talkshow hosts) are overly stoic.