17mm Comparison: Chromatic Aberration
Still at f2.8, here's a 200% sample from a region toward the edge of the image circle to show off chromatic aberration.
|Canon 16-35mm f2.8 (corner)
||Nikon 17-35mm f2.8 (corner)
Clearly better colour control by the Canon, though both are respectable in context of similar lens' performance.
17mm Comparison: Distortion & Vignetting
Rollover either image to compare and contrast the Nikon's distortion and vignetting performance at 17mm / f2.8.
Wide open at this focal length the Canon is better behaved: not only is it better geometrically, it is less prone to vignetting: perhaps half a stop less light fall off in the corners. At 17mm, the Canon has a very subtle waveform distortion pattern compared with the Nikon's more pronounced (but easier corrected) barrel.
The Canon also appears to be wider at an indicated 17mm. The apparent rise seems to be an artefact of the Nikon-EF adaptor.
You might also notice even at this size the more contrasty nature of the Nikon ED glass compared with the Canon L. Given a gloomy scene like this, colour differences are minor. The Nikon on average, though, is slightly warmer, more saturated and, to me, preferable.