My vote goes for Avast! FREE AntiVirus. I am using it from 1.5 years now and it hasn't given me even 3 false-positives (considering my habit of frequently downloading cracked software; often identified as malware - but not a malware).
Avast! Free AntiVirus also has some features of paid-antivirus like AutoSandbox.
Not a good idea to advertise that you pirate software. That's just asking to be banned.
i dont want to buy a paid version..which will offer max protection among the above..
I use Avast, and have no complaints. I've used AVG in the past, but was disappointed in the detection rates. Now, I always use either Avast, or Microsoft Security Essentials. As area51 said, combine it with Malwarebytes, and you should be pretty good.