I wouldn’t bet the odds off just yet. Why i’m always returning from others to avast! are minor details in free edition.

avast! can check for updates every hour. Antivir and AVG can do that only once per day. Imagine the 24 hour time window without any possibility of getting new urgent update (unless by clicking Update button all day long, but i have other more important things to do than this). Just check 18.11.2007 day. 3 updates in few hours timeframe. You’d have to wait for the rest till monday with AVG or AntiVir.
Second is spyware detection. Antivir and AVG free have no such capability while avast! doesn’t make any difference between free and payable. Third is configurability. AntiVir is the only here that comes near avast!, AVG is just too limited.
There is also no nag popups in avast!. That annoying popup has turned me away from AntiVir regardless of how superior detection it has.
And lets don’t forget tech support and ALWIL guys constantly in contact with their regular users (having loyal users, be it free or payable certanly can pay off greatly i think). ALWIL team also takes very good care for regular users that help here. And best of all, we can actually shape the product, give new ideas and so on (quiet some of them implimented are mine and from users like Tech, SasH and DavidR and few others). It’s really a pleasure to use product that has features that fit your needs and wishes.