I'm a relative noob to eReaders. Got a nook about 3 months ago and a Sony prs-900 two weeks ago. I thought I'd post because my experiences with the Sony are a little different than everything I read in all of the "reviews" and comparisons online.
While the nook has a more white screen, I find the Sony much more readable at any font size. This is because the Sony typeface itself is much easier to read than any of the fonts in the nook. The typeface is so good it makes up for the dimmer screen for me. The nook is not a bad device except for it's annoyingly slow touch screen (which I expect will be fixed once their programming team gains some more experience with Android) and it's barely useful web browser.
Regarding screens, in direct sunlight to me the Sony looks BETTER than the Nook because they both look equally bright and the Sony just has a more readable font. Granted, this is the Sony in it's best lighting and when you move to more varied lighting conditions the Sony does not look as white as the nook, but it's STILL more easily readable to me.
Regarding the overall operating system of the two, the Sony wins hands down. The touch screen just makes more sense to me. The Sony also turns pages faster, actually has the ability to go to a particular page number (the nook does not) and the size factor is a big plus for my needs.
On another note, I played with a friends Kindle 2 and while it looks like it has a really well designed operating UI the fonts on the Kindle were not as readable as the Sony at any size. I've got a Kindle 3 on order, so when I get that I may follow up with more thoughts.
At this point though, the Sony 900 is easily more readable to me than anything else I've tried...which is not what I expected. I will most likely return the Sony 900 (30 day policy) and pick up the 950 when it's available...unless the Kindle3 changes things!..
