Biden might have said Hillary would have been a better pick, but I just can't see Obama dumping Biden for Clinton. Why?
1. It will have the look like and actually be a matter of desperation. The public will interpret it as a "me-too" move after McCain picked Palin.
2. It will signify that Obama can't make a real decision without waffling. This is a personal and personnel decision and one of the first big decisions that Obama had to make. You can be sure that McCain will point out Obama's waffling on this simple decision, what will is say about other, more difficult and more important decisions?
3. It assumes that Hillary Clinton wants the job any more. It would be obvious to her and the rest of the world that dropping Biden for her was a desperation move and I am not sure she wants that.
Wait, what was I thinking, of course Hillary would take it--what was I thinking, her ambition is more naked than an entire nude beach.