In reply to Roadrunner5:
> Paul Ryan or Rubio id say..
When Romney selected Ryan as his VP candidate it was largely seen as an attempt to reach out to the tea party faction of the GOP as well as the traditional base. i.e Romney was the moderate part of the ticket. I'm not sure anything has changed.
They need someone who has not yet revealed themselves to the wider American people if they are to heal the rifts caused by the Trump candidacy and appeal to any demographic beyond their traditional supporters (which they need to do to win a general election).
My tips would be Gary Herbert (Governor of Utah) or Brian Sandoval from Nevada.
From those Republicans who already have national status, I think they could do worse than John Kaisch, but he's run for the nomination twice and not got it so there might be limited appetite from him, the party or public for another go.
As an aside I genuinely think either McCain or Romney would beat Hillary, but don't know if they would have beaten Trump to the nomination had they gone for it. McCain is too old.