I would go with the Canon 100mm macro. I think there are now two versions of the Sigma 105mm EX. I think the new versions of the EX 105mm may have HSM and a non-rotating front element, though I'm not sure. The older Sigma 105mm isn't an internal focusing lens and lacks a HSM/USM motor. The Canon will focus quickly, quiter, and the front lens won't rotate which makes it easier to put the lens right up on the glass. I am also not sure if the Sigma lens has full-time manual focus, which I personally couldn't use a lens without it. Optically I hear they are similar though.