My vote is for the Poly. From their beach you are directly across from the castle so it looks like the fireworks are right behind the castle. The music is piped in (you might have to walk around abit to find the best place to sit). From the GF it looks like the fireworks are to the left of the castle - by quite a bit. We have watched from both places and we love the Poly. You are closer to the MK and the fireworks at the Contemporary and you can watch from the 4th floor deck but you are also looking over the parking lot of the Contemporary and I would much rather look over the water to see the fireworks then a bunch of cars.
Linda