I don't have or have never had avo or gaz so I can't speak from personal experience - I was seriously thinking of getting coilovers for my escos but ended up getting koni's and ahmed springs - because I was warned off avo and gaz by Mark Shead and Phil Saunders - and told its only worth paying the 1k or so for leda's (which for me was too much).
After the "advice" I had I read up on PF just to see what other people had said and notice quite a few people had problems with avo - that was enough to prompt me to buy koni's and ahmed springs.