Having put many hundreds, maybe thousands of copies of AVG on home users computers in recent years - I now have changed to Avira Antivir.
Version 8 of AVG has gone the way of bloat and the seed of the idea that your system resources are theirs to control is growing. It is not too bad yet, still a good program that will slow you down just a bit more. But the way they are defensively arguing on their web forums against some of their customers that at least want the option of disabling bloat, does not bode well. Norton and Mcafee were once good programs....
Avast is OK also but bigger memory footprint and requires annual registration.
Antivir has a better detection rate, and uses less resources. Avira are technically excellent while being marketing idiots. By which I mean their program has a popup every time you update. All over the web you will read this as just about the only criticism.
But there is an easy way to fix it here:
http://www.elitekiller.com/files/disable_antivir_nag.htm
I even found an obscure one click fix program that I use everywhere but can't find the URL where I got it from....
Lastly, don't be concerned about the lack of email scanning in the free version - email scanning is actually useless:
http://thundercloud.net/infoave/tutorials/email-scanning/index.htm
I have done a full post here with cleanup instructions if you have problems:
http://www.elitetrader.com/vb/showthread.php?threadid=115313&perpage=6&pagenumber=5 Checkout the next page 6 also for a PS.
Once cleaned up, Avira, Spybot, a router (as a firewall) and the built in Windows fiirewall are all an ordinary user who is just a bit careful what he clicks on, needs. I and most of my customers find the latest 1.5 version of Spybot a pain as it always wants to be in your face. I prefer 1.4, turn off the SD Helper, and scan every week or any time you are concerned.
By the way I run 9 (nine) computers in my own large household with exactly this setup - Limewire (keyword filtered) and torrents running constantly - and no virus problems.