The first and most important reason for choosing Romney is that he, and only he, of the remaining Big Three candidates has any chance at all of beating Barack Obama.
All three Republican candidates left with a real chance are admirable men who would be a colossal improvement on the president: But Obama can still rally his true Believer Base, especially if he drops Vice President Joe Biden and puts Secretary of State Hillary Clinton on the ticket.
The GOP-conservative base could shatter if conservatives stay at home or split from a Romney candidacy. Cain and Perry so far have both totally failed to win credibility from independent voters.
Cain, for all his admirable qualities – and I take 9-9-9 seriously – has all the makings of a classic GOP insurgent candidacy in the tradition of Barry Goldwater in 1964, Teddy Roosevelt in 1912 or Wendell Willkie in 1940. He can indeed win the nomination and/or attract tremendous enthusiasm from his core supporters. But he cannot win leading the ticket. And for all his success and courage in beating cancer repeatedly, the health issue alone will discredit him with floating independent voters.