As exasperating as it is to listen to media people talk about the 2016 election when we've just gone through an endless 2012 election, I have a contrarian POV about a couple of the possible candidates.
I really believe there is no way either Hillary Clinton or Joe Biden will win the election or even get out of a primary although a primary may be possible. Both of them will be in their 70's, both will face younger more energetic opponents in the primaries and general election. The contrast will be stark, much starker than now and I doubt the country will want someone of that age in the White House. Reagan pulled it off, but it is a rare thing indeed.
Just looking at Clinton during the hearings yesterday you could see age taking its toll and it will only be more obvious in 4 years. Joe Biden is a somewhat silly guy and getting older will only emphasize this trait. No matter how much some in the media want this, it just won't happen.