Well now I'm at a computer and can type, Ill say the one thing I didnt like when I used a Nikon was that they dont show a preview of the image with your settings on the screen (when you turn viewfinder view on)
My Canon I can switch to viewfinder mode and adjust my major settings till I'm happy with how the light and depth of the photo are
The Nikon I tried to do the same and it just kep the image that it saw, without altering the image in the viewfinder with changes to the settings (If this makes sense)
That was an older Nikon, probably 4 or so years old now so they might not do this anymore. Its more personal preference, I know lots of people using Nikon's and they like them and they take good photos. but I like the layout on the Canon's, they way they are set out etc.
Only way to find out is to use as many different SLR's you can get your hands on, I went straight for Canon but that doesnt make me right