I personally use Microsoft Security Essentials.
It updates often, it seems lightweight and it seems good at catching the few throjans I've come across without any false alerts.
The reviews seem pretty favourable for it too.
several antivirus i tried but i couldn't reach upto my expectation level, finally i got comodo antivirus installed in my PC it's really awesome, works perfect, i am satisfied with that and i highly recommend that product.
Prevents all viruses, spywares and malwares
Improves performance and efficiency
Fast cloud-based scanning
Detects suspicious hidden files
Protects all the devices.
To know more in detail visit : http://antivirus.comodo.com/