Far as I am concerned, the best antivirus is YOU! Learn more about safe computing and no matter which AV you have installed you will never get infected.
I recommend Avast2015 free version. Why spend big bucks on something that isn't going to save you from infection in the first place. Avast free is my safety net whilst researching the removal of malware and it has saved me many times from becoming infected when trying to access unsavory sites for my research.
With any free version of software, pay close attention as you install the product after downloading or you will end up with foistware that is totally useless to you. The publishers of free software make their money by including toolbars, scanners, registry cleaners, etc. to compensate for the free versions offered.
Following are some really good links to read about safe computing. They might be a bit outdated in some aspects but you'll get the picture: