You've got several options. My best recommendation would be to spend the day (through early evening) at Disney's Animal Kingdom and then enjoy a nice dinner at either California Grill or Narcoossee's (depending on which one is available for that night) and watch the fireworks. They usually start at 9:30, so I'd make a reservation for a bit after 8pm. That way, you can get low crowds during the day, a delicious dinner, and see the fireworks without worrying about getting a spot, the park closing due to capacity, or dealing with other "tired" guests.
Another option would be a full day DHS, which also does fireworks and will be slightly less crowded than the other two. If you mind crowds or long lines in any way whatsoever, I'd avoid MK.