The 17-40 by Canon I have for some time. So why spend twice again for a ridiculous millimeters? The light intensity (2.8 instead of 4.0), well. You need perhaps in concert photography. I thought. After two weeks Rumknipsen with the 16-35, I can only say that this was a good decision, not because of a millimeter. The differences are remarkable in low distortion, coloration, overall impression. I have since a 17-40, well maintained, the circumstances give ... :)