If you are just using a PC go with Microsoft's security essentials. It's completely free and for reviews it does fairly well in comparison to the other major vendors.
If you are fiddling around all day on questionable sites go with a better vendor, otherwise microsofts own product has done very well.
Also, if you are just browsing different sites just use a linux box, or a live linux on a usb drive.
Power off, garbage gone.
http://windows.microsoft.com/en-US/w...tials-download