I would definitely not go to a water park on the 4th - the crowds there will feel much worse.
If crowds bother you, I would recommend Epcot. That park is very spaceous, giving people more room to spread out. There is lots of entertainment, and the fireworks are excellent.
Watching the Magic Kingdom fireworks from the beach at the Polynesian Resort is also very nice - unlike the normal MK fireworks, these shows launch from both behind AND in front AND all around the park. In other words, if you are inside the park you will miss half of the action. Needless to say, the park will be extremely busy anyway (filling to capacity).
The Studios will have Sorcery in the Sky fireworks, which are now only presented twice a year, so that's a nice thing to do as well.