Well the difference isn't that great for me, but it's hard to vote against an album that opens with Aces High and 2 Minutes, and closes with Powerslave and Rime....
This one is much tougher than the other final IMO. Piece Of Mind is a brilliant album, but Powerslave is just a shade better IMO, so it gets my vote....just.
Opens with Where Eagles Dare, Revelations, Flight Of Icarus, Die With Your Boots On, The Tooper and Still Life. Nothing can come close to that.
(Except of course opening an album with Aces High, 2 Minutes to Midnight, Trooper, Revelations, Flight of Icarus, Rime of the Ancient Mariner, Powerslave, Number of the Beast, and Hallowed Be Thy Name.)