I've used Norton, Kaspersky, AVG and other antivirus programs but guess what?
I'm using Avast on my setup and it's been nothing short of wonderful
Note: Yes, I've tried those all in Windows 7 and Avast, as far as performance and reliability is concerned did not fail any on any of the things I put this computer through. And best of all, its FREE! Now, how can you beat that?