Have tried a few
my favorite now is avast4pro mostly because of excellent support, configurability, footprint and safety. My favorite used to be f-secure but latest gave me frequent disk access errors on my raid controller. So for a while i went back too the 5.30 release but as nod32 its missing easy access to deactivation and its slower than avast. Other than that it has stopped everything ive ever thrown at it.
Used Nod32 for a while. I think it is missing system tray availability to deactivate resident shield but in all other aspects i find it to be quite good but perhaps not as much as it is hyped up too be

Symantec corporate 8 crashed when i purposely activated a trojan
Norton av 2002 worked quite well for me but slowed my system down too much to stay.
Avg has its strong points but i find it a little unfulfilling.
Same with kaspersky.
One of my first was inoculate it witch i thought were ok until i went for avg and found a couple of viruses that had slipped through

Also briefly tried out Vet but i felt somewhat more secure with f-secure
Edit: Oh yes also tried out fprot but found its configurability to be way below par.