The beach at the Poly is a really great place to watch from - get there about 10 mins early to get a chair, 20 or so mins early to get one of the wind breaks (at least during off season, would likely need more time during high season).
This is our favorite place to watch the MK fireworks from - you may not hear the music, but it's quiet and private.
Also, try to catch the Electric Water Pagent while you're waiting for the fireworks!