Although, there will be some pressure for him to choose a woman, I think the odds on favorite, now, is Rob Portman.
I think you’re right. The last thing he wants to do is screw the pooch on this—(see McCain, John 2008). He will go with a safe if uninspired choice and will be looking to surprise no one. Also, he does not want a “rock star” who will overshadow him (see McCain, John 2008). Portman it is.