Well my 2p is that in about 10 years Norton is the only one that hasn't let me down and consistently picks up viruses, though I agree it uses far too much PC resources.
I had AVG free installed on a computer at work for a few months, always kept up to date, and when the company IT people came round to check it over they said it had 3 different worm viruses on it which AVG had not even noticed so they put Norton back on! I can only hope the paid version of AVG is better than the free one... the increase in cost of Norton plus the fact that it is a resource hog means that when my laptop's copy of Norton 2006 (the last version that didn't use TOO much of your computer) expires in a couple of weeks, I am going to have to do something else because it will no longer let me renew the subscription - don't know why but it says I need a new "system key" or something, and I don't have anything apart from the key that it came with. Installing Norton 360 would make the laptop too slow so I can't use that.