Ain't nobody gonna mention good old NM of the USAF at WP AFB, Dayton OH USA? I go there on an annual pilgrimage! AF One that took Kennedy's coffin back from Texas, five hangars full of what I think is the biggest and best. I haven't been to them all, but Duxford, Yeovilton, and Forvarsmuseet in Oslo come to mind as others I have compared it to. As well as the Gander, NL North Atlantic Aviation Museum just last month on a much smaller scale.
cheers,
Nigel