I'm convinced Microsoft Security Essentials has the most features of a free anti-virus.
My local IT store swears by:
Microsoft Security Essentials - XP
AVG Free- Vista + 7
Kaspersky - Best Antivirus that you pay for
Norton in my experience bogs down your PC like a rabbit in elephant turd :devroll:
In regards to what I actually use, I use nothing. Let me put forward my argument:
1. Nothing important is done on my PC
2. Scans and updates are annoying
3. I do what I want without Antivirus blocking it
4. If theres an issue, I re-install the operating system from scratch, format the disc, reinstall
Plus Antivirus never seems to block anything anyway, the only program I actually have is Malwarebytes Anti-Malware, it's FANTASTIC!