If we mean unique among their own catalog, the eponymous and first album, RUSH, has to take the cake. I mean, come on: it was Alex and Geddy and JOHN, influenced by Cream, aiming to sound like Zeppelin. That being said, I understand the votes for Caress of Steel, as, it was their first attempt at being seriously unique on PURPOSE. And, surely Didacts and Narpets is the most unique Rush SONG. Edit: but, I'd argue that CoS has quite a bit in common with Hemispheres and 2112.