Norton is the worst memory hog out there I have found. Only thing worse is Vista!
I use, and have used AVG for years myself.
Yeah, it may keep the viruses away, but it certainly sometimes keep myself away to. It's unbearable to use sometimes when the real-time protection goes into overdrive!
I've been using Kaspersky for a few months now and I'm pretty satisfied with it.
But, a friend told me that Kapersky has a trojan in itself. It was said to them in seminar that he attended.
And, after awhile you'll notice some files missing. Well, I haven't experienced my files missing yet. So, I don't know if that is true.
But since my license will be over soon, I might try Avira or AVG since they're free and I've been reading pretty good comments about them.