I compared the then current Nikon and Canon back in 2005 and the Canon consistently focused faster, had less shutter lag, and was simply easier to shoot with. My camera was a D200 and the Canon was a comparable model but I cannot remember which actual model it was, so if my memory is faulty it could at least partially due to the camera being better. Both were (are?) very good lenses but the Canon seemed better to me. Regardless, my main need is the flattest field macro I can obtain for reasonable $ and a versatile flash system, so I'm sticking with Nikon.