Kindle - love it for the following reasons.
Battery charge lasts for a month (with wireless turned on sporadically to get books).
NO GLARE - can read outside in the sunshine with no problem.
Don't have to hook up to a computer to put books on it - when I got mine you had to download books to your computer and then connect the Nook to the computer - which doesn't work if you work for an agency that doesn't allow that hookup on your laptop when on travel.
This fall (I believe it's November) Amazon is putting out a software upgrade that will allow Kindle to work with books in the e-pub format - LIBRARY BOOKS!
I have to say I have friends who have the Nook - they are split - some wish they had gotten the Kindle some love the Nook. I have never had anyone who has a Kindle say they wished they had the Nook.