Prior to 2005 I owned both Nikon & Canon, whichever seemed to do the job, in 2005 I sold my Company & retired, decided to get seriously interested in Photography, looked at which system offered the best all round benefits, Cameras in 2005 seemed much the same Nikon D70s or Canon 5D, but what directed me towards Canon were the Lenses, I didn't feel at the time Nikon had the same range or quality of Lenses, so I went Canon 5D & later to the 1 Series. Although I now have 1Dx, 1DMKIV, 5DMK3 & 5DMK2, I also recently bought the Nikon D800 to replace my 5DMK2 system for my Underwater Photography, seems to work well, crappy write speed of course, but the 36MP has some advantages, but the Menu system seems to have been put together by a Delusional Monkey on Crack Cocain.
Just waiting for Canon's large MP camera & I can get back to all Canon gear, at the end of the day though they are really just Tools, but you tend to make your bed once you get into the Lens side, not hard to jump ship on a couple of Camera Bodies, but a 100k on Lenses ?? I'm with Canon for the long haul I guess.