[ApK]

I've found Norton/Symantec and McAfee both to be tremendous resource hogs, and no better at detecting threats than other options. I've used both AVG and Avast, and while I appreciate free software, their ads and popups became a bit too intrusive for me, especially considering the non-tech types I usually install it for. I got tired of "there's a blue box on my screen, what do I do?" calls.
I've just started using Microsoft Security Essentials, which seems to work as well as any.