Dems will win against any of the GOP crop with absolute ease. Reps are losing their centralist runners, which simply equates to not being able to land swing votes. Whether it's Hillary or Sanders, GOP needs to nuke itself and start from scratch. The whole Paul Ryan fiasco goes to show how extreme they're becoming.
Not a single candidate possesses the charisma to get swing votes. Christie is a piece of ****. Cruz has the likability of a Hitler youth. Trump? Lol. Carson is a ****ing idiot. Bush may have been a decent candidate to win over undecided voters, but we've all seen the dumpster-fire that his campaign has become.
Then you have Rubio, who maybe has a small, small chance-- until you realize that his policies are far too conservative for 2015. He'll lose, just like the others. Romney woulda mopped the floor with this crew. Centralist, charismatic, squeaky-clean record.