It's hard to say because it's so personal, but I have the regular little nook just for reading, as well as an Ipad. And as someone who reads for HOURS at a time, I love the nook a lot because it's easy on my eyes. And if you don't use it much, it stays charged for a month. I can read a week without needing to charge it. And I like the ability to highlight passages, put bookmarks, and instantly pull them all back up. I have always marked up books, and now I can do that electronically.
Since my life is busy, I read where I can. Lunch break at work. At the park while my son is playing. In a matinee movie waiting for the movie to begin. And so on. An e-reader, whatever brand, is PERFECT for this.