If you're planning on using your reader for library books, make sure you check which devices are supported by your local library. I don't believe that the Kindle is currently supported for library use....but that may have changed since I bought my reader.
I have the Sony. It is quite simple and plain, but it does exactly what I need it to do. I am currently reading about 2-3 books from the library per week with it, and it is so easy to use! The best part is I don't actually have to go to the library - which was always easy to do to borrow, but seemed to be a problem to return!! Now, no more overdue fines!!!