I have used Avast forever, it seems, and I have never had problems. I don't even use a Spyware scanner - avast catches everything for me. It updates automatically, it looks cool with all the skins I have downloaded and made, it does not catch anything in my games (killing games is Norton's and AVG's job), and it has many more options on what to do with the viruses. On top of that, the boot time scan is the most USEFUL utility I've ever heard of. I scan about once a week with it while I sleep and I set my computer to shut off in 2 hours.
My only complaint is that it seems to have trouble detecting viruses in RAR archives. That is not a problem though - it catches them upon extraction before they do anything.
~~Ben