Impossible to tell, but I'd still pick Scenes from a Memory as the best album, since it floored me so completely and utterly when I first heard it. On release day. Not even knowing it was Metropolis 2 thanks to not having yet the internet!
Another album that floored me was Trans Siberian Orchestra's Beethoven's Last Night. All the theatrical side of music, I love it because of that record.
Iron Maiden is my favorite band ever, so their two favorite albums of mine, Piece of Mind and Seventh Son of a Seventh Son, both deserve a mention.
Blind Guardian also deserve a mention, with either Imaginations from the Other Side or Nightfall in Middlearth... or both.
Helloween also, impossible to not mention Keeper of the Seven Keys pt 2.
Judas Priest's Painkiller also should be in there.
And Virgin Steele's two "The Marriage of Heaven and Hell" albums are both fantastic.