http://antivirus.about.com/od/antivirussoftwarereviews/a/freeav_2.htm
Avast and AVG do not seem to be good when it comes to detecting spyware. While Avast has a pretty good detection rate, its still not good with anti spyware.
And according to PC World, only AVG and Antivir are in the top 10.
http://www.pcworld.com/article/124475/top_antivirus_software.html
I know Kaspersky usually has the highest detection rate. And I also know Norton slows your computer like a turtle.
Kaitlin