i have never used both, but don't listen to any one on d2jsp they are all canon zealots!

but if i had the choice i would switch to canon, but that would depend on when you could purchase more glass. i am switching atm to go full frame canon, and buy better glass one lens per month.
if you dont have a budget stick with nikon and get that nikkor zoom, im guess this is the year for a d700s so then you will be smiling.