I've spent a lot of time in my college's Computer Repair Lab testing various anti-virus/security suites. We have tested just about everything on the market.
The fact of the matter is this, anti-virus/security suites are not worth paying for. Stick with the free stuff unless there are particular features that you feel you just have to have.
Think of it like this, anti-virus systems are always a step behind the designers creating the newest viruses/malware/etc. They aren't preemptive and can only deal with threats that are documented. Make sense?
It is the features, the rate of updates, the rate/speed of detection, and the ease of use between programs that sets them apart. Sadly, paying for a security program does not make it more effective and generally speaking, doesn't even effect the rate of updates (although this differs between companies).
For regular PC users I would highly recommend that you use either: AVG, Avast!, Panda, or Bit Defender. They work just as well, if not better than anything you can pay for and are simple to use, keep updated, and to install.
AVG can be found here:
http://www.avg.com/us-en/homepage
Avast! can be found here:
http://www.avast.com/en-us/compare-antivirus?cha=aff&elm=ban&var=en_us_homepage&aid=ond_1234&omcid=aff_standard_product&utm_source=oneNetworkDirect&utm_medium=affiliate_US&utm_campaign=aff_standard_product&ClickID=cpa4nal4xpkfslpen4pzpw4epaxwslikniln
Panda can be found here:
http://www.pandasecurity.com/security-promotion/antivirusoffer/USA/?track=109089&gclid=CNTTx5aS9MICFQNgMgodnAIA-w
Bit Defender can be found here:
http://www.bitdefender.com/solutions/free.html
Here is an article with the current rankings for free security suites if you are interested:
http://www.pcmag.com/article2/0,2817,2388652,00.asp