is that the free one?
ESET NOD32
http://www.eset.com/products/compare.php
Can't go wrong with NOD32. Small footprint on your resources, and can't go wrong with it's capabilities or reputation. You can even view the other links within the website on it's performance.
http://www.av-comparatives.org/
http://www.virusbtn.com/
http://www.eset.com/products/compare-NOD32-vs-competition.php
I am using symantec antivirus enterprise edition under university licence. Runs perfectly, auto scran, auto update, never requires me to do anything. It makes vista as virus-free (seems to be) as Mac OS. I recommend it to anybody who can get a public licence. The enterprise edition is way better than the symantec persenal security suit.