I can’t even come close to picking only 1 album; even 10 would be impossible.
I listen to 3 major genres, and quite a few subgenres within each genre. And within each genre and subgenre, there is music that I rate just as highly as in any other choice in the other genres and subgenres.
Jazz - post-bop, fusion, chamber-jazz, avant-garde
Prog - avant-prog, Canterbury, Zeuhl, classic prog, prog-metal
Classical - avant-garde, atonal, spectralism, serial, 12 tone,
I guess if someone were holding a gun to my head, and forced me to name 1, it would be Yes - Close to the Edge (since it was such a game changer in my listening history).
But seriously, there are many albums by Magma, Thinking Plague, King Crimson, Gentle Giant, PFM, Banco, Anglagard, within prog. Mahavishnu Orchestra, John Coltrane, Allan Holdsworth, Anthony Braxton, Return to Forever, Miles, Oregon, within jazz. And Elliott Carter, Alban Berg, Charles Wuorinen, Bruno Maderna, Joan Tower, Stefan Wolpe, within classical, that I consider the equal of any other recording I would chose.