PcMag has done a comparison of the free anti-virus products to see which one is the best. And the one that I have been recommending to all those who I help or ask me is the Editor’s Choice. And that product is AVG Free 2014. You can read on the others that they looked at but let me share that as an IT professional of over 25 years experience and dealing with people whose machines have been infected/compromised by viruses and malware I have found that AVG is the best product on the market. When I have cleaned computers it has been paid products that let the person down. If I put the paid product back on they are usually infected within 1 or 2 weeks again. I put on AVG after cleaning again and I am never called again for an infection. Now AVG offers a paid version, the questions is do you need it? The extra features that they have in the paid is not one that I have found a particular reason to tell customers to go with the paid. Licensing is the issue that you make sure you are compliant with. Last time I looked at the licensing if you have more than 5 you have to pay for licenses.
I would like to note that they did mention a particular product for cleaning called Malwarebytes. It is only for cleaning and not protection. If you are trying to clean-up a computer you will want to try this. I have not used it myself but it sounds like a very effective product. For the full report click here.