I wouldn't like any of those three really. Kaine adds nothing in particular to the ticket (and, as governor, he can help Obama in VA anyway, as can Webb and Mark Warner. Maybe they'll throw Chuck Robb out on the stump as well). Biden is practically guranteed to say something stupid and I think he'd be better suited as Secretary of State. Bayh is the worst.
Sam Nunn brings tons of experience and, if Obama ends up with any chance there, possible help in Georgia. He's also younger than McCain by a few years. I also don't think an experienced candidate takes anything away from Obama's 'change' message. And I want my prediction to be right!
I do think Kerry would be the best/my favorite choice. All my reasoning has already been posted.
Hopefully the latest talk of the announcement still being a few days off is a ruse to keep leaks/reporters away so the mailing list does get it first. I don't want to keep waiting. I really thought one of these guys would have made a pick before the Olympics.