Whoa, I don’t know if this translates to either camera being better over the other, but PetaPixel has posted a video showing slow-motion video of 2 Nikon cameras and 2 Canon cameras as their mirrors go up and down to capture an image. The Canon cameras at the top of the video jiggle and wiggle a lot compared to the Nikon ones below.
UPDATE: I’m an idiot. The Canon cameras are on the left. Still, it’s unnerving to see the mirror bounce like that regardless of camera manufacturer.

The cameras above are the Canon 5D Mark II, the Canon 7D, the Nikon D700, and the Nikon D7000.