I've been using Microsoft Security Essentials, mostly because it has a very low system footprint. I'm mostly ready to jump over to Linux of some flavor, since I use almost nothing that requires Windows anymore. The only Windows machine I *need* is my gaming system. At least until more things get ported to SteamOS.
In my opinion, it's far better to pay for off-site backup of files, Google Drive being my preferred route. Then, should you ever get a virus, it's the NUKE option (reinstall Windows).
I'm only a family and family-run small business employer "IT" guy, not a pro. The few genuine viruses/malware I've run into have circumvented pretty much all the AV vendors and required a reinstall anyways.
But yeah, avoid the boobies :P