A few years ago Norton became very resource heavy so I abandoned it. I won't use McAfee. I tried Avast but didn't like how it worked on my computer. Tried Windows OneCare but it wasn't sufficient. Worked with AVG for a long time but it doesn't work well with Windows Vista. It wouldn't let me access my printers which are either wireless or hooked up via ethernet. There were also problems with Windows Media Sharing. AVG always turned off network discovery and browsing under Vista and their tech support wasn't very helpful. I know it was firewall related but there was no viable solution to get it to work.
Today, All 5 computers on my home network use Norton 360. Its a lot more resource friendly than older versions of Norton and works well on both Windows XP and Windows Vista. Spent a couple months researching, downloading free trials and such before settling with Norton again.