I voted other for AVG.
Although on my own rigs I don't require a background AV, I can usually tell within minutes if a machine is infected with something, seem to have a 6th sense for it. It was back in 2000 I think that I lost faith with Norton, my 6th sense told me my wifes rig had aquired a virus, chernobyl I think it was, so I used the latest trial of Norton and it didn't find it. I used McAfee and it didn't find it. Most people would have thought their rig was clear then. Not me, I got the free fprot that runs from command line, and that one found it and removed it. There seems to be 2 fprots around, one Scandinavian one that is free and a commercial one. The one by the Scandanavians is the good one. It's not so easy to use though and not sure it's updated as often as it used to be, which is why in 2001 I think, I found AVG and started using that as my default virus tool. I've got it set up to run at boot on the kids rig, and just have it installed on my other rigs in case I need it. I run it once every so often just to check.
Strangely enough I've never found a virus on a random sweep. But every time I get that feeling, I've ran an AV and found one. If my 6th sense triggers and AVG doesn't come up trumps though, you bet I will try everything else until I find the bugger.
I have been known to use a disk sector editor to search for and remove virii, but since they rarely have clear text IDable strings in them these days I'm putting more trust in AV products.
On the couple of occasions since 2001 that I've got an infection, where I've had the luxury of time to play, I've found the virus with AVG and left it unfixed and ran other trialware versions of big AVs. It has not been often that they have found the virus!
I've put AVG on other peoples rigs too, they complain about thier PC acting, up, so I go over, sit down in front of it, and tell them, "It's a virus" and they tell me that that's impossible because they always use Norton or McAfee, so then I DL AVG and run it and clean up. One time there were 23 viruses on this one rig that Norton did not see, and 3 that it saw but couldn't remove.
Anyhoo, best AV is common sense and avoidance of reliance on MS. I don't use outlook or IE. I try to avoid the "default" apps for other internet applications as well, most common=most targetted.
Road Warrior