Every controlled test I've seen of the Nikon 24-70 shows more purple fringing around high contrast lines than I'd like, as have some real world photos I've seen. This CA can be fixed in software as long as it's symmetrical, though I've seen reputable reviewers report that their samples also exhibited asymmetrical CA that is not easily fixed in software. There are also controlled tests showing focus blur in full frame corners due to field curvature at long distances, which isn't fixable either. Regardless, I'd prefer the fixable things to be fixed in Adobe Camera Raw instead of Capture NX-D.
A few of many references:
http://www.photozone.de/Reviews/236-nikkor-af-s-24-70mm-f28g-ed-review--test-reportwww.cameralabs.com/reviews/Nikon_Nikkor_AF-S_24-70mm_f2-8G_ED/Also see CA numbers on DXO Mark.
You can also compare to the Canon equivalent here and you'll notice some extremely visible differences, even stopped down, especially in the corners. Mouse over the image to compare.
http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=787&Camera=453&Sample=0&FLI=0&API=0&LensComp=618&CameraComp=0&FLIComp=0&APIComp=0I think the Nikon 24-70 is the best zoom in the range that fits a Nikon, just like Canon sensors are the best sensors that fit into a Canon. Neither fact makes the lens or sensor "stellar", it makes them the best you can get for a particular system. I'm not here to put down anyone's favorite lens, but because I'm after a Nikon system for the sole purpose of improved image quality the Nikon 24-70 isn't the lens I want. I've already decided that the only way I'd do this is with Sigma Art 50mm and 35mm primes plus a Zeiss 25mm prime. I initially said I didn't want primes due to size and weight, but way too much research points to this as the definitive solution. If you compare these, even stopped down beyond F8 to the Nikon zoom, they're clearly superior. They're superior to the Canon zoom too, but by F8 the differences are very small.
FWIW, I'm looking to add this Nikon-based system to what I've got versus switching from one system to the other. I'm not a "fan" of either one, but I'd love to somehow combine the strengths of both, and I also think both have weaknesses.