Age and health issues aside, I’m going with Fred Thompson.
He might not add much to the ticket, but he’ll be there in 4 years ready to be a real president and pick up the pieces of the McCain disaster-to-be.
Either Fred or Huckabee would appear to help McCain in the swing South. Huckabee is younger, but unlike Fred, alienated a lot of folks (specifically, many FredHeads-Who-Ended-Up-Backing-Romney), too.
I’m starting to warm up to the idea of a Fred pick. Perhaps because I supported Fred for Prez, I over-corrected.