Bernie is easier to beat by any two of their incredibly flawed Repub candidates, especially after the angry, ugly, and lying campaign he's been slowly ratcheting up for months (since December, actually) now.
Hillary is our only chance to not only win the White House for another eight years, but to also get a Democratic Senate, Governors mansions, and legislatures - not to mention, a progressive SCOTUS! She's the strongest candidate we have, and she knows how to get things done because Republicans in the Senate and House know how she plays the political game, and they're terrified of her.
Even the punditocracy on teevee fear her. They've mentioned more than once how the Clintons are known for hitting back 18x harder when attacked. Hillary knows where the bodies are buried and which of their closets have skeletons, and she won't hesitate to use these weapons should Republicans try the same crap with her as they've been doing with President Obama. She's a natural born warrior through and through.