Rekd, I think you are too biased. You are also manipulating the the advertising. Though I shoot Nikon, I do acknowledge that Canon is better for sports, but where are all the pics of people at those events with Nikons?? Trust me there ARE plenty of them. And ALL your pics were of Canons at sporting events. So is that the only thing Canons are good for? What if the OP doesn't have any interest in sports photography?
Back on topic: Nikon or Canon?? Well you answer me this: Mercedes or BMW? Lamborghini or Ferrari? They're both great. But if I had to choose, I would say Nikon because you already have a really nice, and expensive Nikon lens to go with it.
Note: For the record I own neither Canon nor Nikon. I own and use Leicaflex.
For the longest time (let's say from 1965-1989), Nikon dominated press and PJ work, which had before that had been dominated by Leica rangefinders. Topcon, Canon, Pentax, Minolta, Leicaflex and others were also-rans. When Canon came out with fluorite lenses, the F-1
http://hifishack.com/images/canonf1_5.jpg
and then the New F-1,
http://farm2.static.flickr.com/1077/608897943_3ebd6c9e14.jpg
they were clearly showing their intention to do something serious. Though Pentax and Minolta showed some initiatives toward 'pro' models, they were largely ignored. Nikon was clearly the leader in press work.
When Minolta finally introduced auto-focusing in 1985, they dropped their old mount altogether and started from scratch. When Canon introduced their first auto-focusing line in 1989, they followed suit, thinking (I suppose) that the advantages of starting afresh far outweighed the disadvantages. The new lens system offered far more potential, which owners of the old system would surely see.
Nikon made some tentative steps toward autofocus in 1986 or so, but the F4 was not introduced until 1988. It was a monstrosity by any measure.
http://static.photo.net/attachments/bboard/00S/00SMKC-108487684.jpg
When Canon introduced the EOS-1 in 1989, they seemed to have made a authoritative statement about what an autofocus pro camera should be. It was designed from the ground up as an autofocus system.
Canon EOS-1 - Main Index Page
The press market clearly and immediately embraced the Canon, as everyone has mentioned. Nikon, by retaining its lens mount from 1959, was afraid of offending its customer base. But when you don't have much of a customer base to offend (Canon) you are not constrained by them. Sure, it would have pissed off some Nikon owners if Nikon had changed mounts completely...but in the long run everyone would have been better off.
This short-term thinking that affects Nikon had effects that persist to this day.
Sure, you can use a 1959 Nikon lens on some of the current Nikon pro models, but
so what? Any lens that old is going to be outdated.
Nothing lasts forever.
If you compare the F5 or F6 to the EOS-1V, there is in my mind no comparison.
http://www.luminous-landscape.com/images/EOS-1V.jpg
http://www.kenrockwell.com/nikon/images1/f5.jpg
http://www.apertura.cl/store/images/f6body%20nikon.jpg
The F5 and F6 are clearly a retreat from the monstrosity that characterized the F4.
Now when digital came out, things didn't change a whole lot. Canon made a full-frame DSLR body based on the ESO-1 fairly early on. It took Nikon a decade or so after that to have one.