As you will probably be happy with either choice then ergonomics should be a high consideration. I played with a few Canons and Nikons in the shop prior to my first purchase (a D50) and again recently when I upgraded (D200). For me, and it is personal choice, the Nikon "fitted" my hand better with the Canons not being comfortable at all. I have quite big hands and the Nikon were far more comfortable *for me*.
Go and play with some for a while in a shop and see which manufacturer suits your hands - then decide
after all you;ll be holding it
a lot!