How to choose the best free Antivirus Software for you?

I've been looking at this link:

http://www.pcworld.com/article/170674/free_antivirus_software.html


Avira AntiVir Personal
Alwil Avast Antivirus Home Edition
AVG 8.5 Free
Microsoft Security Essentials
PC Tools Antivirus Free Edition
Comodo Internet Security
Panda Cloud Antivirus
PC Tools Threatfire
ClamWin Free Antivirus


How do you determine which free antivirus software is the right one for you?
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