Obama can't pick Biden because he looks like a crook, and at the same time looks like he should be on the top of the ticket instead of Obama.
He can't pick Sebelius, because any woman except Hillary would send Democrat women into a frenzy, plus she gave a response to the state of the Union that could have been given by a skeleton robot.
He shouldn't pick a General or Sam Nunn because the overwhelming compensation for his lack of experience will shine through.
He can pick Kaine, but it would be a big mistake because it would result in a no experience ticket.
Bayh or Jack Reed seem most logical. Both have experience but don't come off as Washington insiders. Though I don't think Reed offers any electoral help, while Bayh could get Clinton's people on board, which could translate into Clinton voters for Obama.
Hillary? At this point, why not?
Darkhorse pick that would make a lot of sense. Senator Ken Salazaar from Colorado. Why? He is from a swing state that Obama needs, plus Salazaar won there in 2004 not the best Democrat year. He is Hispanic which could instantly increase Obama's Hispanic support. His brother is a Congressman from another Colorado district to help at the grassroots level to win CO. And finally he has been in the Senate for since 2004 without spending half of that time campaigning for the White House, so while he doesn't have an abundance of experience he is not a newcomer, and he was Attorney General of Colorado for 6. Experience without D.C. He won't pick him most likely but all and all and interesting choice.
Finally, its probably going to be Bayh
After proof reading this it seems like every candidate should be on the top of Obama's ticket. I mean even Ken Salazaar who many would consider under experienced to be President spent 6 years before the Senate running a Statewide Justice Department while Obama spent his time organizing communities(doing nothing) and being a State Senator (which only requires a pulse, and some corrupt Chicago pols on your side).