The best scanner is the one you have the most luck with. There have been many surveys, and none agree on the best AV suite with a resident shield.
The best scanner and remover, is Clamwin. It does not have any resident protection. You have to manually scan with it. In other words, the best of the best Virus removal tools out there, has to be installed before you are infected and can only help you after you are infected. It cannot block an infection from happening.
There is Avast, NOD32, AVG, McAfee, Symantec, and more. If you keep it updated, you will find that each can protect your system equally. The issue becomes one of resources. Symantec products look great, but eat up so much of your system resources, you would almost prefer an infection to your protected and slower computer. The Free edition of AVG offers the same anti-virus and anti-spyware protection as the paid version of AVG, just lacks all the bells and whistles and extras that seem to "sell" the product.