It's a huge debate isn't it? What's better anyways? Some people prefer to use Norton Antivirus and others AVG. This article is going to go over my person experience with each and hopefully help you decide which is better for gaming.
I will be using:

1. Norton Antivirus 2008 (w/ Windows Vista)
2. AVG Antivirus 2011 (w/ Windows Vista & 7)
3. Norton Internet Security 2009 (w/ Windows Vista & 7)
4. Norton Internet Security 2011 & 2012 (w/ Windows Vista & 7)

    Lets start with Norton, since I used it before AVG. To be honest, Norton was hell.
    My biggestly problem that I always had with Norton was Game Maker 7 and Game Maker 8 games (GameMaker 8.1 didn't cause this issue). Everytime I downloaded a Game Maker executable (.exe file) with Norton enabled the game would immedietly deleted. This is annoying. Being a developer and a player of these games I would download several of these a day. Each time I had to temporarally disble Norton; it is possible that I could've downloaded a file with a virus though. Most of my issues with Norton were the similar to this.
    Another annoyance I had was that if I was on a standard (non-administrative) account (on Windows Vista) Norton wouldn't run. I never could solve this.
    I had some other issues but my only other MAJOR problem was that Norton would stop working whenever I launched Civilizations. :( That makes me sad!
    There were two annoyances with Norton. This first (only pertaining the Norton Antivirus 2008): It would always give messages about high CPU usage on everything. The other (with both) is that updates are annoyingly frequent, but at least I'm assured my antivirus was up to date!

    Now, onto AVG! AVG is my current Antivirus so I will do my best not to be byass on this article.
    One of my issues with AVG is that it is too anxious to give me wanrings about my C++ programming. It's not really an issue, more of a major annoyance
    A real issue is that it blocks network communications for applications and granting permission doesn't always work so I'll need to disable it.
    AVG interferes oddly with programs sometimes and I will have to disable it.
   
    So, personally I do prefer to use AVG. In Norton's defence I never got a virus with either, so they both are effective. For gaming I had less issues with multiplayer gaming while using Norton, AVG does not like applications with internet communications.

Hope this has been a bit helpful in your antivirus shopping!

- Nikc-Nack