Hi Alex,
If you want to know which one is best, try to know yourself best first. You should find out what you need and what you want to do with them and decide which one suits you more. Anyway, you can't get everything you want from either one of them. You need to compromise. Some people hates to admit that they have made wrong decision choosing a certain brand and then they would say the brand they are using is very good. If I say which one is best, will you accept? If you know your need well, you will find your best camera. It's not Nikon nor Canon. It's you.
By the way, each of them have particular attributes (such as what "rendition" mentioned). Many people may say Nikon has good built but if you have better feel with Canon, who can stop you?
If one of these two brands is more advanced in every aspect than the other, the other has long gone out of business already. To me, I am just glad that these two are very competitive and we can get our camera with cheaper price since either one of them can't monopolize the market. Brand is important, of course. However, it's more for the company. Do more research on your own. Wish you find the one that best suits you.