I have both a kindle and a nook,

get the Kindle over the Nook, Nook has few apps,and
you're limited to buying books from Barnes and Noble on it.
Kindles have an almost unlimited supply of free books you can get EVERY DAY. Seriously, 100's every day. If I could go back in time and re-choose a tablet it would be a Kindle for this reason.
Amazon has won big time with the free content for Kindles, the Nook is a pale comparison.
( i currently use a Nook color with a 'root' sd card installed so I can use it like a kindle. funny,huh?)
Now if you are buying books for the reader the prices are about the same, but B&N has very few for free. Amazon has hundreds daily.
If you're buying for dgs to just READ on, I suggest a kindle with paper like screen and glow background, hands down,the simplest most elegant way to read books,IMHO. My ds has a simple Kindle reader(no light) and he reads more now than he ever did previously.