I use avast, which isn't in the poll. I used Norton for several years, but got tired of paying those annual fees. I tried Mcgafee once but tossed it into the bit bucket because I couldn't see the buttons on their dialog boxes and was unable to resize them so that they would show up properly.
kaspersky is the best anti virus i have ever used! doesnt have all those update pop ups and doesnt consume much ram usage.
the best is truely KAV and KIS they provide the best possible security and believe me I have tested all know antivirus software out there and founk KAV to be the best however it is a little problematic in vista as it checks all new programs on first start to give them a danger rating otherwise it is the best ever in the field