Online Armor Free has always been my favorite, but if it is no longer an abandoned product, which will soon
Comodo is very easy to handle. If you are one of those who use P2P , is the less it will cost set also has Sandbox. It is the most used and also consumes very few resources
ZoneAlarm free is perhaps the best currently no continuous messages , consumes few resources ...
To accompany Qihoo 360 (having HIPS and Sandbox ) recommend ZoneAlarm free for another antivirus that does not have these features , I recommend Comodo