From what I know of the guy, he seems extremely reasonable, which is what I'm most interested in. I'm pretty centrist, sort of repulsed by the extremes on either side. Hillary is definitely pretty hard core Dem, and that's going to hurt her because the country is kind of tired of this partisan crap, we need someone with a fresh outlook, fresh energy, and willing to go out on a limb for the best interest of this country as a whole. From the candidates, Obama has all that more than the others.
PErsonally, I see a charisma vacuum in McCain. And Lieberman always seems like he's kind of whining. wouldn't be my choice.