We actually found 2 locations we like. One, was the as the above poster stated. Just to the right of the HUB, on the Tomorrowland Bridge. Tink goes right overhead.
The other place we really liked, was just inside the main entrance to MK, go through the locker rental place and stand right there at the top of Main Street. You have a straight on view of the castle, and all the effects are spectacular. Plus, it made getting out of MK a snap, we were in front of most of the crowds, and always made the first resort launch back to FT Wilderness.