The only people that should care what anyone else buys should be stock holders in that company. They both learned to make optics from the Germans during WWII. The German teachers brought cameras to photograph their travels. They both introduced their first production camera in 1948. Each new model since then has some new feature that the other doesn't have. So, at any given time one might have the edge over the other. For most of us the decision to buy one or the other is economic. We have an inventory of one manufacturers lenses that we can't afford or can't be bothered to replace. There are some idiots in the world that think everyone should own what they own. Maybe to validate their own decision. They probably have an opinion on Fords vs Chevys too.
While Canon and Nikon have been the leaders for a long time there are now many other choices. So if you're looking for a new camera, don't ask here. You'll just get a bunch of BS. Read the reviews. fondle the hardware and make up your mind what's right for you.
Remember I said those Germans, that came to Japan to teach, brought cameras? Look at daddy and his two children by different wives.