There are two ‘official’ locations at Baltimore Washington Airport it seems.
From a recent report, the best one is that inside the terminal. This overlooks most action, though some will be missed on Runway 15L. There is also a preserved nose section from Boeing 737 c/n 19307 here.
The other location is to the south of the airport, under the approach to Runway 33L. Aircraft approaching Runway 33R can also be noted. You can reach this spot from Dorsey Road. It is not ideal as registrations are hard to see and photography is even harder. You are also have very limited views of any aircraft on the ground or departing.
Credit to Darren Kellett for the report.