The LEAST harmful candidate would be Ron Paul. Next Bob Barr. And that is just those who are in one of the 3-4 largest Parties.
McCain won't garner a majority of the Electoral College. The Dems voting for him now will cross back into their camp. It'll be Dole/Kemp all over again.
Paul and Barr won’t get squat and votes for them at this point are by default votes for Obama. If there were any chance for a third party candidate who was remotely conservative I would vote for them, not for the party. Republican or any party politics is of little interest to me and has little meaning at this point. What is of interest is the single candidate who will do the least harm to the constitution since that is the only choice the degenerate primary process has left us. If I thought that Obama would do less harm then I might at least not vote and let the election fall to him by default but that is certainly not the case, he is the biggest threat to the constitution, a bigger one than McCain.