When comparing Canon to Nikon, three main aspects of these camera brands always comes to mind - camera build, picture quality, and lens.
First, let’s take a look at camera build. Both Canon and Nikon cameras have their distinct characteristics when it comes to the camera body's design and make up. Be it a DSLR camera or point-and-shoot, it's hard to tell which one is better than the other one. Although I could attest to the fact that when comparing their entry level DSLR - Nikon D20 vs. Canon Rebel 350D, I noticed that Canon is slightly heavier. Build-wise though the Canon Rebel 350D is more professional looking than the "toy-like" build of the Nikon D20. The same goes true with their point-and-shoots. My first Canon digital camera was the A400. And I could definitely say that it was on the heavy side. And I have personally used a friend's Nikon point-and-shoot before and couldn't help but notice that it is lighter.
But that's just the weight factor. And you might prefer a heavier camera than the lighter ones. So again, it's still a matter of preference. Although if we are to judge Canon and Nikon point-and-shoot cameras on portability, Nikon will certainly beat Canon.
So, we might as well move on to another interesting point of contention when it comes to comparing Canon and Nikon - picture quality. Now on this one, I would have to say Canon beats Nikon big time (I'm sorry Nikon fans, it's my personal opinion). I have seen different outputs of the Nikon DSLR and point-and-shoot and cameras and compared it with the outputs of my own cameras and I could definitely say that Canon camera's picture quality are way livelier and more realistic in color.
Nikon tends to overemphasize on the deep color of its output so much so that the picture quality tends to become "over processed." Don't get me wrong here, there are many photography enthusiasts and photography audience who prefer to see more vibrantly colored photos. This is well and good, although the naturalistic effect is lost.
Another discussion point when comparing Canon and Nikon is lens speed. Some say Canon has faster lenses than Nikon. Interestingly, Nikon fans themselves tend to agree with this. But how important is a fast lens in photography? Does it affect photo quality? Well, you can always adjust the settings to offset the effect of a slower lens.