I answered earlier regarding my Nook and being somewhat satisfied with it, but wishing I had waited to get the 'glow' one.
I'd like to expand on that answer now.
For daytime reading the Nook is superb.
For nighttime reading I prefer using the Nook app (or whatever other app) on my HP mini. I've found that for nighttime reading I also prefer to not have much other light on in the room except what is on the computer screen. Others prefer it with the room well lit.
It all comes down to personal preference and what works best for you.
Try out as many as you can and then make a decision. Not sure how you will be able to simulate a semidarkened room when in a store though.