So, how do I choose??

In term of choosing antivirus for your computer, first of all you need to identify your usage, whether for light or heavy usage. If you just using your computer for e-mailing and normal use, free antivirus just enough to keep you and your family protected!
Unless, you have learned from your past, free just not enough! Or you use your computer heavily, sticking your friend's thumb drive, downloading modifier (crackers), dealing with anonymous and uncountable high-risk activity, so you might find that paid antivirus is more reliable.

So how do I choose? Before you make up your mind, first step is to try the multiple antivirus from different developers and make some comparison. Don't just try their free package of protection, instead go for 30-days limited trial of their premium protection suite.