I have used all three, not at the same time of course. I liked AVG8 but found it slowed my system. I tried AVAST but didn't care for it's interface, personal opinion really. I now have used Antivir for probably 6 months. I like it quite well. It updates regularly. Free version does not allow for scheduling scans but I don't mind doing them manually once a week or more often if I am concerned about something.
It's really just a matter of what you like really. I am pleased with Antivir protection so that is the one I would recommend but had not complaint about protection factor of the other two either.