hi may be this will help you choose. these are all good av softwares, prices may differ where you are as these prices are from India, where i am.
this just a comparison and i would recommend trying free trial versons of all reputed AV programmes including the free ones and check which one suits you coz they all have good features and it only depends on what you like to use.
and make sure you dont rung more than one at a time so uninstall previous one before installing new programme.
http://anti-virus-software-review.toptenreviews.com/