In addition to Ariel484's excellent recommendations, I strongly recommend you choose a nighttime spectacular at the DLR as they are very different from the WDW offerings. You may have to choose between World of Color at DCA and Paint the Night parade at Disneyland, but those are good choices to have.
I've been to WDW 3 times since 2006 and have seen the exact same fireworks show at the MK all 3 times. Disneyland is currently on its 3rd fireworks show in that same time period.
And if Disneyland brings back the wildly popular Hyperspace Mountain overlay after Halloween this year, it is spectacular.