The Case for Romney
Clearly, there are candidates with a longer track record of conservatism to choose from. There are also other candidates who would arguably make the ticket more "electable" by delivering a big state or constituency.
So why is Romney a good pick for McCain?
When you factor in philosophy and pragmatism (the need for a solid conservative successor -- as well as the need for someone who can bring something to the ticket electorally speaking), Romney probably makes the most sense...