If he isn't the nominee, it'll be Kasich. If Kasich is the nominee, it'll be Rubio.
I don't see Fiorina or Carson. Carson's got a compelling narrative, but could he really be President with no political experience? Fiorina's the kind of candidate that seems real qualified, and she could do the job as President, but she'd be the type to make a gaffe in the form of showing her corporate aggressive side that would get her the kind of negative play that Romney's 47% comments got him. Kasich expands the map for any candidate, and a Kasich-Rubio ticket might be a real map-expander.
Real qualified? By what standard? Losing a senate race and running HP into the ground?