AV-Test in Germany is one of the top research facilities in the world for testing anti-malware protection. 24 different products were tested on over a million samples collected in the past 6 months. All testing was on Windows XP SP2.
Only four products gave them all a clean bill of health: Symantec, McAfee, Microsoft and eTrust-VET.
See the the result at http://blogs.pcmag.com/securitywatch/Results-2008q1.htm