The thing about an SLR is that switching brands later is hard. Yu but the body then a couple lenses and then wheat you buy next has to be that same brand. Switching means selling everything and starting over.
I switched brands a little over a year ago.
My motivation was in the fact that I've always considered digital complementary to film, but my main film system(Canon FD) was incompatible with my main digital system(Canon EOS). I know that I COULD have bought a good EOS film camera or two(the EOS 3 came under strong consideration) I ultimately decided that I didn't want to completely give up manual focus and all mechanical cameras.
For peaceful co-existence in the same bag, that made Nikon the only choice for me.
I don't want to think what my total Nikon investment is now. It's a LOT higher than my Canon FD mount investment ever was, but then I have more disposable income now. I'm easily in the low 5 figure category, and that was buying virtually everything used. In fact, the only new Nikon item I've bought was the dandy little 35mm f/1.8 DX lens-it was $150 for a used one in the local shop vs. $190 for the open box display model with a full warranty and the lens hood(the used one didn't have that). This is normally a $200 lens anyway.
My experience with modern Nikon bodies is mostly with the higher end ones-I use a D800 as my main DSLR, an F100 or F5 as my "film with modern lenses" body, a D600 as my back-up, and occasionally a D2X and D300s. Oh, I also have a Fuji FinePix S5 that serves for quick and dirty "studio" work(Ebay photos, other routine photos under studio strobes). I actually used a D200 in that last role for a while, but found the dynamic range difficult to live with while the 12-year old S5 is better in that department than many modern cameras.
In any case, I find the high end Nikon bodies straight forward and intuitive. I can pick up an unfamiliar one and have it pretty well set up to take photos the way I like in a couple of minutes. The only thing that sends me to the manual(or the internet) are new features or things that are cryptically named in the menus. In fact, it's a LOT better than setting custom functions on the F5, F100, or N80-unless there are certain ones you set all the time, I'd defy anyone to do it in-camera without the manual or at least a cheater card. Fortunately, with the right hardware you can set them from a computer.
By contrast, I find that it takes me a lot more button presses and a lot more trial and error to set up a high end Canon the way I like, although the common settings are easy enough to find. They're in different places and sometimes use a different operating philosophy, but ultimately CAN use one without much trouble.
Both brands are equally easy to use at the low end if you stick to "green box" or scene modes. I give Canon the edge, though, if you want to move into modes where you have more control over the camera. That's only true at the low end, though-by the time you hit say the D7x00 series Nikons I think the ease of use shifts.
I'll also add that switching back and forth can an infuriating experience as-going even back to the early days-EVERYTHING is reversed on the two cameras. You start noticing it the moment you mount the lens-when looking at the lens mount, you align index mark on a Nikon lens at about 2:00 and turn it counter-clockwise. Canons align at 12:00 and turn clockwise. From your perspective operating the camera(eyepiece facing you) infinity is fully CCW on Nikons and fully CW on Canons(with the exception of the Nikon 45mm f/2.8 GN). For lenses with an aperture ring, Nikons are at their largest aperture fully CCW, and Canons fully CW. On cameras with a real shutter speed dial, CW(looking down) goes to higher speeds on Nikons and CCW goes to higher speeds on Canons. On "two dial" cameras, the rear dial is primary on Nikons and the front is primary on Canons(also, by default, the rear does shutter speed on Nikons and the front on Canons).
I'll add too that my main other system is a Hasselblad 500C, and the lens mounting, aperture ring, and focus all the same as Canon's direction. It throws me off to switch. My Mamiya RB67 doesn't bother me as much since the lenses are breech lock and the ring turns the same direction as on Canon breech lock lenses.
