You know, it's a matter of familiarity for me. I owned my first canon 35 mm film camera when I was 18 yrs old so I've just stuck with that brand ever since. Now I'm so heavily invested in lenses and camera bodies that I'm locked in for now. I do love Canon though and am very happy with my 5d Mark II. It's a remarkable camera. Not perfect by any means, but I find the canon to be a more intuitive system with the layout and menu configurations. It just seems to "fit" me better. I have heard that the nikon focusing mechanism is more accurate though. I highly recommend trying out both systems and see which one feels right for you!