None of the above. You use free AVs, don't bitch if you get infected.
click comparatives, review February and May results.
If you want a solid antivirus with decent detection rates, NOD32. Just remember that it's a good idea to use it with an AntiTrojan/AntiWorm product as well.
If you want comprehensive protection, Kaspersky 5.0 Personal is a solid app with broad detection and access to an extended database which includes pornware, adware and other riskware. It's also pretty light on the system, unlike 4.5.
P4 2.6C, Thermalright SP94/Panaflo 92MM M1A, IC7 Max3, Swifty MCX159, 1GB Geil PC4000 Ultra Plat, Radeon 8500, Audigy 2, 2X WD Raptor RAID 0, WD 250GB SE, Plex 708A, 166SDVD, LianLi PC75, XP Pro.