Personally, I don't care a whit who Mitt Romney picks as his running mate. It will have exactly zero impact on my vote in November.
But I am interested, because I'm reasonably certain that there is money to be made on this at Intrade. I don't think it will be Rubio (past with Mormonism, and as many years in statewide office as Sarah Palin in 2008), Christie (he won't do it), McDonnell (too socially conservative for the general election), or Ryan (he won't do it either.) Those are Intrade's top 4 as of this posting.
I'm not certain who it will be. But I am thinking about buying up some long shots while they are trading low, and shorting the (current) top 4.