Right now:
1. Hillary Clinton
2. Jeb Bush
3. Donald Trump (if America wants to do, so be it)
4. Joe Biden
5. Marco Rubio
(6. Bernie Sanders)
(7. John Kasich)
(8. Martin O'Malley)
(9. Scott Walker)
(10. Mitt Romney-you never know, brokered convention?)
Honorable mentions: Paul Ryan, John Thune (brokered convention?), Rand Paul (Underestimate Libertarian voters at your peril), Mike Huckabee (Values still matter in this country in some areas)
I forgot to include Rand Paul, but I would not underestimate him. Libertarian voters are key in this country.