DisplayMate tested the screens for Screen Reflections, Brightness and Contrast, Colors and Intensities, Viewing Angles, Display Backlight Power Consumption. There's a 6th category, Running Time on Battery, but DisplayMate hasn't recorded any figures for the battery life of the Kindle Fire or Nook tablet.
There was no single winner of every category, but the Kindle Fire did consistently come in second or third place in most categories. And more often than not, the Nook Tablet came in first place.
The iPad 2 and Nook Tablet didn't get raked over the coals nearly as much as the Kindle Fire. In fact, aside from the technical differences in the screens, there was hardly a bad word about the 2 tablets. The Kindle Fire, on the other hand, was faulted for software issues and for having a highly reflective screen. The display on the KF was so bright that it reflected significantly more light than the iPad 2, and over twice as much light as the Nook Tablet.
The KF is a new device, so it probably comes as no surprise that there are problems with the software. DisplayMate noted that the KF is using 16 color in the Gallery, not the 24 bit color seen elsewhere on the KF and on other tablets. The Gallery also showed serious issues with grayscale images.
Now, the software issues could be fixed, but there's not much anyone can do about the highly reflective screen. Well, you could use it as a mirror so you could brush your teeth, but there's no practical way to reduce the glare. DisplayMate cautioned against using a screen cover to reduce the glare; they say that it fuzzes out the glare with a matte finish.
P.S. When I approach this from a technical point of view, the data is fascinating. I love highly detailed and intricate reports on which is better. But from the user view point, I'm not sure it matters. I've had both tablets on my desk, and I couldn't really say that one was better. They were both such a significant improvement on standard LCD screens that I've seen on ereaders and tablets that the differences were imperceptible - to me, at least.
What did you think of the screens?