Norton used to be absolute crap, apparently they've turned around and are now actually pretty good.
AVG is the opposite, they used to have a decent free product but now its more bloatware then anything.
McAffe is still garbage.
Trend Micro and Kaspersky are both great paid choices.
Microsoft Security Essentials is the free one that I recommend these days, not as good as the paid ones but it is free.
I have set up Windows 7 with auto updates and Microsoft Security Essentials on my family members computers and have yet to have them come back to me with a virus...