Upload & Sell: Off
It all depends on the first camera you happen to buy. 99% of people just stick with what they're familiar with. Both systems are perfectly capable of delivering amazing results under the right situations.
That said, each brand certainly has things they do better. (Until the D800) Canon was decidedly better for landscape, architectural, product, (stationary subjects) and their color might be a bit better, also their sRAW file format is a HUGE plus for their users. Nikon however has an advantage on AF, especially in poor lighting, and their menu and button layout are a lot more user friendly.
Like almost everything else in life... tomayto, tomahto.