i use avg for free, but it's not full aplication, if you use avg premium, its so good, or you can use norton n360, its so good, very good. i recommended you for buy it.
Symantec Anti-Virus: Corporate Edition It gets the job done without the constant hassle of expiration and updates.
NOD32 works for me. i used to use norton then but eats up a lot of my pcs resources. NOD32 very light and dependable one
Can't beat ESET Nod32. After trying a multitude of virus programs, this is the one I continued to use due to the simplicity and the low memory usage in comparison to other AV's. It's a perfect Anti-Virus for older machines!
I don't use any anti virus. From my experience i can tell such programs don't do anything to advanced viruses they just make your system slow. I suggest just to keep away from sharing media and files from others computer without knowing it's ok and keep away from suspected website and files online.