I have a dual-boot configuration over my computer, I use BitDefender over my Windows 7 installation and Malwarebytes Anti-malware over my Windows Server 2008 R2 install.
I have been using Avast free home edition for about 4+ years now, mostly without problems. My current PC has been running for around 2 years without issue.
Just be sure to disable all sounds as it can be very annoying.
I used to run ZoneAlarm for one year.
Now that I don't get my self ratted alot, I don't use one.
KIS 2011 seems to be really good. I trust in Kaspersky since many years.
avast ! been the best for me since I discovered it
I use AVG as I feel that best!
avira is simply the best..!!
been using a few diffrent ones.. but the one i usally use is avast