I haven't really used anything other than AVG which I haven't had a problem with. However, from what I've heard, antivir is pretty decent and so is Nod32, haven't really heard much about avast, but then again I haven't really heard about much about them as a whole since I mostly just stuck to AVG for when I'm in my windows partition, and most of the time I'm in OSX anyways, so it doesn't particularly matter.