I tried both. Sigma drove me nuts. The Sigma zoom ring turns in the opposite direction than the Nikon zoom ring. If you shoot action and zoom with muscle memory, it get confusing and frustrating, when you keep turning the zoom ring the wrong way. I gave up in frustration after 15 minutes. But, if not fast action, then turning the zoom ring the wrong way only cost a little more time, not a lost shot. The Tamron zoom ring turns in the same direction as the Nikon zoom ring. So Sigma for Canon, and Tamron for Nikon.