Bitdefender Free. Light weight, cloud based and pretty good. I have never had an issue with it. But if you use game hacks and such you don't want Bitdefender Free. In fact, you may not want an anti-virus at all. I don't run an anti-virus on my gaming computer in fact. And when I say game hack I don't mean cheats, I mean mods and such. But game hack/cheats will have issues with a Firewall or anti-virus too. Believe me. LOL
I need to mention that definition-based anti-virus isn't that effective anymore. I would in addition to an anti-virus use Sandboxie for your browser. Just keep in mind that if you update the browser you have to do it without Sandboxie. And I would allow access to the browser's profile folder so addons can update. That would be at reduced security however. Also, scan downloaded files at virustotal.com