Can't imagine a Universe where I vote in a Democratic primary ever, so I would vote for Huckabee so that he is the one who gets destroyed in November, allowing an electable moderate conservative - who faces far less pressure from the base to tact right on cultural issues - can make it through the primary in good shape and beat Obama in 2012.
Romney was basically the moderate you want, though. A different one wouldn't have beaten Obama. Nominating Santorum in 2012, though... Maybe that would've had effect.
Romney took a SERIOUS lurch to the right in the primaries on many social issues, especially immigration.