We use autoblocks on the bottom, prussiks on top, multiple stopper knots, and butterfly knots every 6 feet that each person unties and then reties. It takes us 2 hours to rap a 25' drop, but we're super safe. :D
A few years ago after a long multipitch climb, I did about 25 rappels on a sheer rock face in Yosemite in the dark. You can bet your ass we used stoppers each time. Ironically, we forgot to untie one of the knots on the very last pitch and had to come back early the next morning to retrieve the rope.
I liked the folks at Zion Adventure Company in Springdale, who were knowledgeable and friendly. I think they and other companies around Zion usually do single-day tours to Birch Hollow, which we strongly considered. If I were in Zion, I'd feel good with them.