Actually I have been using AVG now for about a month or two on my own systems and I find it to be very light on resources as apposed to Mcafee or norton. I infact started a back to school special where if the customer does not have antivirus software or wants to free up some of the system I will install it for them. And feel free to check out my site and give any sugestions... LOL but I guess I can't post my site yet... Oh well I have a few more posts to make.
Best Software is Nod32 made by eset ( eset.com) when downloading updates it only has 2 percent cpu spike and only takes up 30 mb you can also run it from a flash drive. Its not free but it worth every penny.
I definately agree with Kaspersky, next up I would say CA. Norton is one of the first things I uninstall when I see it on a system. Hell, uninstalling norton a LOT of the times actually fixes the problem.