I've tried both Kindle and Nook and my experience with Kindle was a lot better than my experience with Nook.

Kindle is user friendly and it gets out of the way as an electronic device once you start reading a book. Nook feels unpolished and awkward in your hands.

Sure, Nook has some edge over kindle with things like a small touch screen (which I found is rather unusable), expandable memory and android. But Kindle does a much better job at being an e-reader than Nook does.