@korkamann,
I admire Elizabeth Warren, Bernie Sanders, and yes, even Biden; yet, in my personal opinion, Hillary Clinton is the only force that can face the GOP and win. Hillary is no stranger to attacks and the way the GOP stole the election from Al Gore in 2000, well, that would never ever happen to Hillary Clinton!!!!!
Hillary is not a people person; she tend to be rather taciturn, not the overly friendly type, but she is a serious individual. Because of her public demeanor, being private, many people distrust her, especially with the GOP piling on their dirty rhetoric that she cannot be trusted. Yet, no one can point to one thing that shows Hillary cannot be trusted. I would rather have someone with Hillary's obvious faults, i.e. rather closed personality, than Elizabeth Warren or Bernie Sanders, although I like and respect these two.
As to Biden, well, let's face it, he's no spring chicken at 73. Is he expected to serve just one term? At any rate, Biden has tried to run two times before and were rejected both times by the American public despite his likability. There is a great deal of talk regarding his dying son's wish that Biden run again. I don't know how true this is, not being in the room when all this took place, but this much I do know, Biden is a politician, and has tried a couple of times before and I see that desire has not left him; if he personally perceives a real weakness in Hillary, he might jump in, but that doesn't mean he could win against a Republican rival.