Here we got the best three free antivirus software for windows ,most of them have exactly the same features and detection level ,however its comes down to the personal preference when selecting better one .and checkout how we rated them.
avast! Free Antivirus

avast! Free is our choice for the best free antivirus software ,worlds most used free antivirus, it’s just outperforms from the above two competitors with lightweight design , less memory usage, less false positive detection ,and an awesome user interface . and the boot time scan is also helpful feature that makes avast standout from its competitors .
Download avast! Free Antivirus
AVG ANTI-VIRUS FREE EDITION

AVG is playing a great role in home users for years ,but still we found the user interface is not that friendly as avast ,but a good free antivirus solution for home users who looking for more features from a free antivirus ,and the great thing is there is offline update option in avg ,which helpful for users with no internet connection can easily update it by manually downloading virus definition files from avg website.
Download AVG ANTI-VIRUS
Avira AntiVir Personal – Free Antivirus

A light weight antivirus software best for slower computers ,but we found Avira is too sensitive to some files (and making some annoying beep sounds )and the false positive ratio is greater, but overall a small antivirus program for user with really slower computers ,and it has a offline update option ,which is helpful to users with no internet access ,we recommend Avira to users with netbook,slower laptops and slow desktop pc.
Download Avira AntiVir Personal
avast is my all time fav & it is installed on my pc since 2 yr with no problem….
Thanks for the list, I guess I will settle for Avira, my PC is not to up-to-date really.