No, not Romney. Chris Cillizza makes the case against McCain picking Crist.
Crist's appeal to voters in Florida is based largely on who he is, not what he stands for. His detractors attribute his high favorability ratings to the fact that his chief governing philosophy is based on doing whatever is easy and popular. Crist defenders insist that he is a compromiser by nature, an approach to governing that rank partisans might not like but that voters respond to.
Still, Crist's passion is clearly his populist pitch not his policy chops. At the national level, Crist would be challenged far more often than he is in Florida on his stances on issues and his own proposals on key public policy matters of the day.
And, given that McCain's appeal to voters is far more dependent on his personality than his policies, it might make sense for the Arizona senator to choose someone who adds policy heft to the ticket.