http://www.lensoftruth.com/head2head-call-of-duty-black-ops-ii-screenshot-comparison-wii-ups3xbox-360/

My opinion looking at the pictures...

360 >  PS3  = Wii U (? PS3 version have more details in screen).

360 have more details, better textures and cleaner look (less blurry).

Edit - I checked the pictures again... the PS3 have more details than Wii U too.

http://www.lensoftruth.com/heads-up-call-of-duty-black-ops-ii-analysis-wii-ups3xbox-360/

Performance analyst.

FPS: 360 > PS3 > Wii U
Screen tearing: Wii U > 360 > PS3

The only pic that shows more details in the PS3 version is the forehead of the colonel.   The Wii U version shows more details, higher resolution textures and no stupid green fitler.

XBox and WiiU are very close, hard to say which is better. PS3 is clearly inferior though.

XBox = WiiU >> PS3.

DF confirmed.

http://www.eurogamer.net/articles/digitalfoundry-black-ops-2-wii-u-face-off

Visual: 360 > Wii U > PS3
Performance: 360 > PS3 > Wii U

Overall: 360 > PS3 > Wii U * the Wii U performance is really bad sometimes half of the framerate *

Just to guys here said the Wii U version have better resolution (720p)... the Beyond3D's guys said all version have the same resolution with the PS3 version decreasing the resolution in certain parts.

PS3 = 880x720 (dynamic? Instances of 832x624..., post-AA) 
360 = 880x720 (2xAA)
Wii U = 880x720 (2xAA)