Also, I heard that you would tour the grounds of Hogwarts as well as the school itself. One of the rumored scenes, that I have heard from the very beginning, is the Whomping Willow scene from Chamber of Secrets.
Anyway, as for my scene, which I find discussion strangely lacking of, I picked the Chamber of Secrets. Because, since the land is supposedly going to be based off the first four books, I'd say that scenes with the greatest chances are most definitely prevalent scenes from the first four books, and Chamber of Secrets, in my mind, is probably the most prevalent from the first four.
Any other scenes that pop up will probably just be to set the scene of the ride, I'd imagine, or move the story along. If I were a betting man, I'd say the climax will probably be in the Chamber. ;)
Regarding the ride system, I have to agree with Raul and Dan so far. Suspended can mean a few things, but robot arms suspended from the track leaves me guessing right now. Keep in mind....riders can be considered "suspended" even with the Kuka arms attached to a ground track. I believe I have seen floor prep work in some pictures taken that might confirm this, but like Robert said...with Universal things can always change with a blink of an eye!
I chose the staircase. If they could elevate and weave you through it like you were a camera in the films, with the stairs narrowly dodging you and the portraits all yelling at you, it would be fantastic.
I wish it would end with the final confrontation between Harry and Voldemort in the Great Hall, but that part of the movie won't even be out yet.
The Troll attack would be good - maybe it could follow the cars around from time to time, then swipe at them similar to Exp. Everest's Yeti?
Would be a shame not to pop "outside" briefly to watch a Quidditch match, but that may be another ride in the land.