The one in DC is really great though, you may want to consider doing both, there are many extremely historic planes and vehicles there including the Apollo 11, Mercury and Gemini capsules. Apollo 11 was the one that involved the original moon landing, the lunar lander is there as well. There are several historic planes like the Howard Hughes racer (not the spruce goose), early WWI planes, cold war missiles including some soviet union ones, and just too much to name. What's cool about the DC museums is most of them are all right there together and you can walk to that one then do the Natural History one which is walking distance. NH is my 2nd favorite, its the one with the dinosaur bones and stuff.