My own rule is very simple: 1) support the most conservative & freedom loving candidate; 2) in the general election, support the candidate with the best chance of defeating 0bama.
Number 2 means you’ve already lost.
That's basically my approach too:
Vote offensively (for the best candidate) in the primary.
Vote defensively (for the candidate to the least damage) in the general.
IF you want to win a war, first you have to win some battles. You don't win battles by sitting out...