I would hope that the first qualification is someone who isn't lying to us, who won't change their tune the first day in office. That leaves out Romney.
Gingrich is out too, he might believe what he says on any given day, but it tends not to be what he believes and says a week or two later.
I trust Cain will surround himself with good people, and have access to the best intelligence, and make good decisions based on that intelligence.