The NEC and Dell have different panels, one 27" and one 30". Unless you compare to the Dell 27".
They all ( including the Apple ) have the same panel, LG I think. The difference is the backlighting and glass or matte coating which are different on all 3. From my experience with the Dell U2410 and what I have read abt their 27" and 30", it all depends on your intended use.
I do some photography and video, but also work in an office that I can easily control the light. If I could redo I would have bought a refurb apple 24" even for $120 more than my Dell. I don't know the effects on my eyes but the screen window muddy effect bothers me when I open photos.
Pixel density obviously is different from my previous screens but the matte is the same or worse than my 2003 PowerBook.
I'm not a fan of Apple Glassy but since I can control my lighting, the Apple is much better for photos.
That said, you have to think about the audience of your work.
For web work, who are your viewers? Corporate or consumer? The whole consumer PC industry went glossy years ago to sell shiney Vista PCs. All modern Macs are glossy too.
It couldn't hurt designing and developing on the same type screen that most of your viewers are going to use.
Sorry I can't answer your question but I am also considering an Apple 27" ACD or same size NEC. I am not considering the Dell from present experience for my uses.
For basic use, Excel, Work etc.. The Dell is fine, just not what is ultimately right for my needs.
Hope this helps