I've had a Q-jet, edelbrock 600, and demon 625 and 725. I didn't know how to tune the q-jet. So I have no real feedback there.
The edelbrock is a great beginner carb, if you're new and want a basicly drop and go carb. They're the one.
The demon is equal to a holley...the main bore area is different, the bowls and parts interchange. I like my demons, once I jetted them correctly and put spring needle/seats they work great. I used holley parts btw.
I've heard good things about the truck avenger though, with the anti spill thingy.