You would think the 150mm would be better since it has more "reach", but it just isn't worth it, IMO. You can still only get 1:1 magnification with the Sigma and the minimum focusing distance is 15". The pictures will have the same magnification but you will just have to stand farther back. I personally press the lens right up to the glass when I don't want to use a tripod, the 15" focusing distance would really limit my shooting options. The Canon 100mm is a tough piece of glass to beat.