PANDA is miles ahead of everything on the market, it has removed viruses from my computer that had AVG and NORTON could do nothing about. Free anti viruses ? 'Free' usually comes with a hidden cost, such as the cost of getting a new computer !
Kaspersky has one of the best scanning engines and is more effective than the likes of Norton. Second best is BitDefender.
I had experimented on all major antiviruses but still my PC was infected with malware,trojans etc but since i started using escan internet security i'm free from virus,malware etc. since 6 months.it has many features like password protection.As we all know 1 in 8 attacks comes from usb ,Escan has a great feature of password protection.and automatic scanning. when you plug in any usb you will require to enter password.so in this way there is two way protection.i.e protection from virus and also data theft.there are load of features.i would recommend for it. If you want to go for free then go for AVG,or Avira also install malware bytes free version along with the free antivirus.install all the updates too.of ur OS