Importantly, both courses make you think about each shot you play.
Shinnecock makes you think about the demands the course puts on your game, and, accordingly what shots you can or should hit in certain situations.
The National, however, more so than SH makes you look at the course, and decide among which shots you can play.
Shinnecock, to me, more than any other course, with the exception of, maybe Winged Foot, is really a series of "Hobson's Choice" shots. No such limitation exists at NGLA.
For that reason it is NGLA.