Pyro
Epcot has the most spectacular fireworks on the 4th (and New Year's Eve). On those two nights, they plus up the regular show with additional pyro... including, I once heard, a second chance finale for all of the 'duds' that accumulate through the year.
Also, the park has plenty of room for everyone. They always have special entertainment all around World Showcase as well.
While you're down here, though, be sure to catch the fireworks at MK one other night. The new show is called Wishes. Everyone says it's great... and in the summertime it should be on every night. Check the entertainment schedule as your trip approaches, though.