Avai is standardized and is much easier to use.Ditto that. I personally find that the THX patterns are very difficult to get right. Of course, they are free with the movie, so you could say that they are worth what you pay for them.
If the cost of Avia is a problem, get the Sound and Vision HT Tune Up. It is essentially a subset of Avia at about 1/2 the price, PLUS, I think I read that it had DTS test tones, in addition to DD.