"There is an argument against using any antivirus software at all."
Avast! with it's exclamation mark is not that well rated
AVG comes out pretty good
That's the free stuff
Pay-for-it, they rate Avira Premium Software Suite (above McAfee Total protection 2009, F-Secure Internet security 2009 and Norton Antivirus Gaming Ed 2009)
See also http://www.av-comparatives.org/