I love the B&N Nook Simple Touch.  I can't compare it to the Amazon Paperwhite, because I refuse to try one.  The Nook has expandable memory (which I do not believe the Paperwhite does).  Up to 32GB, which means I can save around 32,000 books.  If, for some reason, I need more space, then I can just drop another 15-20 bucks, and have another 32GB (though I will have my collection split over two memory cards).  I also like that B&N accepts ePub, which is pretty much the universal standard, whereas Amazon locks you into their own store.  This means that you can shop Sony's store with a Nook, and Nook's store with a Sony, but Amazon can't access either of those stores.