I use AVG personally. If your machine is so infected with a virus that it's become impossible to clean, you're much better off just formatting the drive and reinstalling. You don't know how deep the virus could be hiding or what it's really doing behind the scenes. Until the computer has been completely wiped, it may as well be considered totally compromised.
Make sure you have a good backup and then just wipe it. I know it's a pain in the ass, but it's really the only way to make sure it's clean, especially if your virus scanners are having a hard time cleaning it.