You really can't compare one or the other. Comparable camera vs comparable camera... they are about the same. It really comes down to personal preferences.
However,
For 2012, reports from JD Power & Associates show that the Market share is preferred Canon about 10% over Nikon. BUT... Owner satisfaction/reliability goes to Pentax, with Nikon coming in second. Canon trailing in third.
So, if you are looking for the answer by power in numbers... then you might want to consider the Canon because it's more popular and more people are buying them. However, according to the numbers, if you want a camera that will last and satisfy you... get a Nikon.
LOL, I can't wait to see the replies to this one