NOD32, not only is it effective but its also light on the system unlike some solutions starting with 'N; that seem to overwhelm and take over your PC as if they own it and antivirus is the only reason you use an OS.
kaspersky all the way...Really good security,,,The firewall, antivirus all of them rock,, and i run it on my laptop and i doesnt tax the system one bit...
I Have Been Using Kaspersky For Many Years Now .For All The Bitdefender Fans .Bitdefender Uses Kaspersky Technology To Run .But Has Souped Up Interface And Has Many Added Advantage .I Have Really Never Used It .