Overall, the NEC looks better especially since it has an A-TW polarized filter for less white blooms when viewing off angles. NEC's internal electronics improves color uniformity a little bit. It's OSD menu is also a bit more robust, there is a "power user" mode which offers you a lot of options to adjust colors. In case you play games, the internal video processing that the NEC performs causes the 2690WUXi to have an average input lag of 33ms.
The Planar is a great monitor especially if you are rather reluctant to cough up the extra $400 - $500 for the 2690WUXi. I recommended the Planar to a friend of mine who does professional graphics presentation for a living and he is extremely happy with it. It lack the extra electronics that the...