I have used Norton and QuickHeal anti virus but i was not satisfied with these anti virus so i bough Avast anti virus and its working great.
According to my opinion Avast is the best anti virus for PC protection. i have use this anti virus for 1 years and their is no complaint of this anti virus .
I too use avast (free home edition is available) it can be downloaded for free and you too can obtain a registration key for free.
The best commercial Antivirus software are Kaspersky, ESET NOD32 and Symatec Norton. AVG, Avast and Avira are good ones in free antivirus category.
I cannot say which is the best anti-virus, but when it comes to free programs, Avira AntiVir has been good to me. As I described it in an article I wrote on PC security: "...[Avira AntiVir] is quickly growing in popularity, and rightfully so; it is a lightweight on the machine, its interface is easy to use and makes good sense, and it has impressive detection rates. If you can put up with the pop-up upgrade advertisement the free version presents after every auto-update, get it."
Norton 360 Its the best PC Protection software. It works great in my PC and Now Norton is giving 50% Flat reduction in their Products as a Holiday Special. Use always your own Licensed product atleast for Antivirus. Premium products are really good compared to that of Free ones. In Free ones the Antivirus Company itself use your PC to test the latest viruses and this threat is not available for Premium Product users.