This may have been done before, but who knows! Anyway, mine would have to be The Moor, closely followed by The Leper Affinity. Too bad they never play The Moor live, I think it would go over quite well!
I find Still Life to be the more coherent of the two concept albums. Maybe it's just because it's the one that has completely clicked for me, while on MAYH I've yet to appreciate April Ethereal, The Amen Corner and Karma
I love The Moor, except that i find the intro taxing when i'm just listening to the Moor, though it's fine when I'm listening to the whole album