For anyone who has never seen the fireworks before, Id suggest trying to brave the crowds at least once in the Hub or on Main Street for a head-on-view. After that, you can pretty much see the fireworks from anywhere in the parks. It is only the preshow segment splashed across the castle front you will miss by a side or back view.
I personally prefer to watch the fireworks from behind the castle in between the carousal and Philharmagic. This allows us to tour up to the last minute without needing to stake out a spot ahead of time. It is also never very crowded back there. We usually just pick a spot and sit on the concrete. I love watching the 360 fireworks from back there because you are almost in the exact center of the park, so they are all around you. They also go off very close in front of you and behind you. The only problems with this location are not being able to see the preshow and not being able to rush out to the buses. However, this never bothers us as we usually loiter until the last possible minute taking pictures in front of the castle, then shopping in Main street, before finally heading out to the buses where by then the crowds have become manageable. Id rather get back to my hotel a little later, than get trampled by the crowds rushing to the buses at park close.