Rubio.
Because youth + diversity + handsome factor > professional accomplishments + experience
Case in point: Obama vs. Hillary '08
What accomplishments did Hillary have? Though I see your point - Biden was one of the few on that stage that actually had professional accomplishments, and look how well he fared.
Marrying Bill Clinton?
I mean that's basically the only reason she is considered a serious candidate if she runs. Otherwise she'd be as credible a presidential candidate as Evan Bayh was in 2008.
Because Evan Bayh was secretary of state for four years, and also ran in a long brutal presidential primary campaign where he won the popular vote.