You should check that all your current and probably future lens requirements can be met on the Nikon mount. Canon has a bigger range.
I'm pretty simple, I just want the basic primes, 24, 35, 50, 85 etc...I know Nikon has some of those and a few choices in each.
One day I might want a zoom or two, but thats too far down the road for me to worry now.
Again, I'm still in the unsure phase, I need to get my hands on a Nikon and play, so thats my goal right now. I might hate the ergonomics of it completely.