Got away from both Norton and McAfee early on, ate too many system resources and etc...
Used CA for years, back when it was free and continued into the paid product when that went away. Then CA AntiVirus changed versions and started causing GPF's in Win98SE box, and actually did BSOD on new XP box: it takes quite a Bad Thing to totally BSOD an XP box with software alone.
Anyway, been using free AVG for about 4 years now, no probs at all.
I use free Avast on old 98 laptop, though, since AVG not compatible.
Depending on the current virus defs, most any AV proggie will give a false positive now and then, which often explains how one AV will "find" something and one won't. Then when virus defs are updated, that often goes away. AVG's are undated just about daily.
I do NOT run the link checker part of AVG, though. Slows surfing down too much, even on fast cable connection. I run McAfee Site Advisor with Firefox as a prelim site check.
Far as spyware, I switched to SuperAntiSpyware some years ago as main checker. In spite of the chintzy sounding name, it has gotten better reviews than AdAware and/or SpyBot for some time. I do NOT run it resident, however.
YMMV,
- OS