Others here have said they have had an excellent view from inside of the castle. Anywhere around the front of the castle is also great, I know a lot of people stand on the bridge to Tommorowland. When we were there, we had a great view of the show from right next to the Walt and Mickey statue. I'll try and include a picture below. The castle came out blurry in all of them because the camera was on fireworks mode, but it'll at least give you an idea.
We enjoyed standing between the right side of the hub off of Main Street and the path to Tomorrowland, on the circle part there. We selected it because my daughter wanted to see Tinkerbell's flight.