Canon for me. Sam, in the cameras = cars equation - which one's which? Is Canon Holden or vice versa?

To be honest, I think at the pro level, it comes down to personal preference (ie: what interface you prefer). The specs are more or less on par.

I've noticed that amongst the two, the Canon professional range seems to be favoured by commercial photographers, whereas Nikon is used more in photo-journalism. Which would perhaps imply that Nikon has an edge in flexibility across all conditions. Without having used Nikon, it's hard to judge, but I've noticed that the Canon digital capture has some artifacts in low lighting and high contrast conditions, which would support this.