Ah yes I forgot to mention the Air & Space Museum on the National Mall in central DC. We got free tickets online at 0830 on the morning of our visit (none available to pre-book for several days in advance). Their largest halls are still closed and the remainder of the museum was very crowded (hence the ticketing presumably), and the catering setup was a bit of a joke (expensive, little choice, almost nowhere to actually eat etc). There are still some good displays and it's worth a visit if you're interested, but if it's a choice of one or the other I'd definitely prioritise UdvarHazy 🙂