Anti-Virus software on jr2's hatelist:
Both have failed to detect viruses in the past (although, that was a long time ago). Also, I have seen both FUBAR a system when they uninstall incorrectly and get stuck in a state of not being installed (so they can't be uninstalled), whilst also still being resident and half-active in the system (so they can't be re-installed, "please uninstall old versions first", etc) and also the internet is usually borked, as the firewall is half-uninstalled or has gone into a paranoia state of self-preservation. (Useful, but usually doesn't get the viruses, they usually manage to shut down the AV soft and firewall.)
*Note: these are the opinions of jr2. They are not to be taken as a unilateral statement of fact. Please don't get hyper-defensive if your favorite AV software is Norton or McAffee.
Personally, I do like AVG (now, anyways, they've improved a lot). But I like MS Security Essentials even more (I've switched to using them, as they've cleaned up the issues they initially had.)