I’ve been using AVG for about 3 years now with no issues. It’s caught plenty of email virii and several malicious scripts while searching for cracks.
It’s update is pretty resource intensive and they update pretty much daily so your first login of the day might be a little slower. But even then it’s only about 30 seconds or so to update. It’s using 360k of memory just sitting here, compared to 70meg for rtvscan.exe, norton’s real time engine.