Conan has Patton Oswalt, Howard Stern, Jimmy Kimmel, David Letterman, Stephen Colbert, Tina Fey, Ricky Gervais, Quentin Tarrantino, a lot more talented humans above 40 and really, any human under 40.
BUT Leno has Paul Reiser and his son. All in all, pretty equal.
For the best response rebuttal to the Reiser-torial above, please listen to the AV's Hater podcast about it. I love the Hatecast so much, for consistently making it okay for me to really hate certain children.