Both Nikor and Canon has compartible lens in terms of optical quality. However, what bothers me is that Nikor lens are just tad bit expensive than Canon ones. Canon lens are also more popular, especailly among photo journalists. You usualy saw a sea of those white barrel, red logo L lens carried by photo journalists. Another measure is to check out http://www.fredmiranda.com/ site and look at number of reviews for Canon and Nikor lens.
Here are the summary page for Canon prime lens:
http://www.fredmiranda.com/reviews/showcat.php?cat=2
And here is the summary page for Nikor prime lens:
http://www.fredmiranda.com/reviews/showcat.php?cat=12
Again, compare the number of reviews.
At this day and age, lens choices are rarely technical: they are all very good. Your technique has more to do with the photos you took. However, choose brand is still a headache because the large amount of investment you have to put down. Just like buying a car. Any car can get you any where you want to go. But you do have to do your own research.