A Ryan choice is a top-shelf selection, but he is not going to cause a significant voting bloc to switch choices. He will give the voters who were going to vote for Romney anyway a new reason to feel better about their choice. Rubio or West, on the other hand, just might bring new voters into the fold.
Welcome to the age of identity politics, like it or not.
Ryan or Trump. I'll duck arrows here, but Trump would get the 'I love The Apprentice' crowd to vote for him. That's just how bad things have gotten but Romney needs to swipe a few wavering 0bama supporters and Trump can do that for him. It's all about getting the insurgent dictator OUT of the White House. That's job one, whatever it takes.
I do believe that Ryan would energize the base and be the overall best candidate. Trump would also energize the base to the extent we really need to become a 'business-friendly' country again.