For my family the answer would be EPCOT. But we happen to like that we can walk to our resort on a night that is really busy. We dread the thought of having to ride a bus from MK. So I guess the best place will depend on quite a few things.
Are you staying at a WDW resot?
Last year MGM had special fireworks. They only do them two times a year, can't remember what they called them. They were terrific. Going again this year and probably will be at MGM on 4th of July.