I've had good luck with AVG. People like Kaspersky, but I bought it legit from the company years ago, and after a while it started getting a little buggy, slowing down my comp, etc....when I uninstalled and installed a new antivirus program, it picked up a trojan with kaspersky in the filename I never went back to kaspersky. I ended up having to nuke and pave the hard drive.
I used to use avg but now I been using avast and to tell you the truth, avast is one of the best av protection online. I never have any slowups and it works like a charm, always catching new viruses before it hits my system.