On the basis that "Should own" encompases stuff you would never really normally listen to then, I'd go for "Gong" "You", the day it clicks you realise that, no-one has ever made the follow up to that album. Recorded over the three days of the full moon and mostly assembled from live takes in the studio, it is both perfectly wrong and perfectly right as the same time. You could easily label it "Trippy hippy dribble" and yet, it has some of the most insane time signatures and absolutely on point individual performances within its grooves. It, like the worm Ouroboros ends up eating its own tail. I only wish the recent remaster, which is superb, was available on vinyl. For me, it is to psych/prog what "Kinda Blue" is to jazz. It might never speak to you, you might never embrace it, one thing it will never do, is sound the same each time you play it.