If I'm shooting seriously all day, I lug my Nikon D200 or Canon 5D.
I prefer my D200 for action and news, and prefer my Canon 5D for ultra-ultra wide angle lenses, landscapes and crapscapes.
My D200 is faster because it operates much faster and more intuitively with features like Auto ISO, and I have a Nikon 18-200mm VR lens which lets me shoot everything with one lens. I can turn and fire, and my D200 always gets the shot without having to twiddle settings.
If my subject sits still, my 5D has better static image quality. If I have the time to twiddle the settings., like ISO, manually or use a tripod, my 5D wins. Canon has nothing similar to Nikon's 18-200mm VR, so I need to bring at least two lenses everywhere. If I have the patience to deal with it, the image quality for large prints is far superior from my 5D, although the results are identical at normal sizes.
Because my 5D is full-frame I can get crazy ultra-ultra-wide results with my Canon 14mm lens, which no one can do at any price on Nikon's smaller sensors.
I own and use both (Nikon and Canon) daily. Which is best depends on what you intend to do with the camera.