they're all useful, none are useless, cuz u need em all to get the Fierce Deity Mask. But the only mask which is truly useless is the circus leader mask, because you get it after it would have been useful. Literally, the only use for it is to make it easier to get the hug from Cremia and have Link's face in her bosom. Of the non-transformational masks, I love the Bremen mask, I love the march song. Its mad stirring.