Not on the list here, but I would have gone with John Kasich. Also from Ohio, but doesn't have any of Portman's vulnerabilities (Kasich didn't serve in the Bush administration, and Portman's gay son could have been disqualifying to the base when it came out, which it would have had he been selected as VP. Kasich didn't have that problem). Also would have carried Ohio, and possibly Pennsylvania and Michigan as well.
Kasich's popularity in 2012 still hadnt recovered from losing the 2011 special election