Pretty much any covers Hendrix and Lemmy Kilmister have done, but beyond that I'm strugling with recalling any covers that are outright better. Entombed has a very good cover of Under the Sun and Voivod cover of 21st Century Schiziod Man is also very good, but neither is explicitly superior to the original. Also if you want to hear a Snowblind cover done properly, go listen to the one by Sleep, the SOAD one is utterly vile and hateful, and so is the Killswitch's Holy Diver cover.