I would definitely try to see it from in front of the castle for your first time. It is so breathtaking, and I think you get the picture perfect full effect.
I've stood right near the partner's statue as mentioned. I also think if you moved back a little bit down Main Street, you'd get an even better view.
A lot of people try to score a spot upstairs at the Main Street Train Station - there are seats, it's a straight shot down Main St. to the castle, and you get a jump on the crowds to head out of the park when Wishes is over.