I'd recommend you use Microsoft Security Essentials for the majority of your protection. It's free, but is very good at keeping you safe. The next two are also free, but they have paid subscriptions with supposedly better programs for sale. They are Malwarebytes ( .org. ) and SUPERAntiSpyware. It doesn't really matter that much whether a anti virus protection is freeware or a paid subscription, if you're careless about web sites you visit or links you click on, you can still get viruses, malware, trojans, and spyware. I've had both types of protection and see no difference in the freeware I use now.
My personal opinion.