I loved AVG. However, I updated to version 8 which included a lot of extras and it took almost 6 hours to scan my computer!
I switched to Avast, and use Spybot S&D. (If you Google Spybot S&D, there is a result that looks a lot like it....make sure it is the real one!)
Spybot removes spyware, which comes in through the computer's "back door", and tracks your surfing habits, as well as taking up extra disk space. Also...viruses CAN come in via spyware, though I've not heard of any cases in particular.
Norton was on a friend's computer that I was working on...what a PIG to uninstall!!! It's like removing a squid, and then searching for the tentacles that broke off in the process. It's a resource hog. One of my geek friends says Norton is a virus itself in the way it acts.
Avast and Spybot - that's my choice. Have had no virus damage at all in over 5 years.
"Common sense and a sense of humor are the same thing, moving at different speeds. A sense of humor is just common sense, dancing." -- William James