Choose whichever you deem best like i said google:
http://www.techradar.com/us/news/software/applications/best-free-antivirus-9-reviewed-and-rated-1057786
http://www.pcmag.com/article2/0,2817,2388652,00.asp
and i am sure you will find a good detailed opinion here if you search for it
I use AVG...