I have used a paid solution for several years now but have never actually paid anything. I have used trials and giveaways and currently I am using Emsisoft Anti-Malware after using Eset for the last year. If I had to use a free AV I don't think I would have any issues as I have used Avast Free and Comodo in the past with no problems.
Easlier I used Avast Free. Now with the help of awesome members of Malwaretips I am using Emsisoft Anti malware Promo for 6 months. After 6 months I am sure I will get another promo for another good antivirus. If not good products like Avast, Qihoo are always there.
or maybe you just don't know that you were infected.
Please don't take offense to my comment. I'm only trying to make a point.
I'm a Cyber Security Analyst and for many, many years, I've heard quite a few of my clients say "My computer is fine. I've never been infected." In most of those cases, I scanned their system and found one or more infections. My supervisor at one company also made the same claim.... with the same results. The point is, we can never be 100% sure our systems are not infected.
Using Bitdefender IS, technically a paid AV but I got the licence for free. So far so good, sometimes quite buggy but other than that I think it's a very good AV and the detection is quite good too. A nice mix of their behavioral blocker and signatures.
Paid : KIS 2015, although most people don't like it but I use it for 4 years and in my opinion is the best. before I use the KIS, I have tried avira free, avg free, Avast, SmadAV, Norton IS and ESET. I even get a promo 9 months of norton IS contained on bundle purchase VGA 2 months ago(I do not use it, just take the bonus game watch dogs)