Kindle Paper White is my primary for all the reasons stated by other owners and I keep my books synced with my iPhone Kindle app for those times you just get stuck waiting. Amazing how much you read in a day if your current book is always in your pocket and synced to the book you read at home.
Also a fan of
eReaderIQ you can tag authors or books for when the price drops and you can sign up for a custom daily mailing of free and reduced price books that match your profile. They also have an add on for Chrome to make it easy to tag books and check past pricing.