eBook readers: Kindle app or Barnes & Noble?

I am a ferocious reader and I absolutely love books. That said, hacking down billions of trees just to make paper seems increasingly irresponsible, and a gradual migration to eBooks is probably inevitable. I've had the Kindle app on my iPhone ever since it came out, and have downloaded and read dozens of books on it. Unfortunately, the shorter battery life of the 3GS compared to my original iPhone means I am using the iPhone less often as a book reader (especially on long flights), but I haven't given up on the concept just yet. So if you like reading books on your iPhone, what's the best way? As is, while I like Amazon and the Kindle app, Barnes & Noble remains a formidable force in the book market and so I decided to check out the Barnes & Noble eReader as well. How do they compare?
The free Amazon Kindle app rocks. It's simple and minimalistic (though a bit less so than in the beginning) and rock-solid. You can select from five text sizes and three text colors (black or sepia on white, and white on black). You "turn" pages by flipping left or right, and the effect is that while you flick or drag, you can see part of both pages, as if your gaze were moving from one page to the next in an open book. I find that very intuitive. Authorizing books is a non-issue--as long as your iPhone is registered as an authorized device, there are no further passwords or codes.
The Kindle for iPhone app has a 3-star rating in the app store. I'd give it a four.
The Barnes & Noble eReader is also a free app for the iPhone. You need an account at Barnes & Noble and you need to authorize a book after you buy and download it. Authorizing consists of typing in the name and card number of the credit card you have on file with B&N. I don't like that at all as I certainly don't want to submit my credit card any more than I absolutely have to. It's probably safe, but still a very bad idea.
The Barnes & Noble eReader's home screen provides access to book shopping (brings up a iPhone-formatted website in Safari), your online library at Barnes & Noble, and then shows major categories. If you list all, they can be listed alphabetically, by author or by date. If you turn the iPhone to horizontal, you can also leaf through the book covers Apple OS X-style.   
When reading a book, you go to the next or previous page with a horizontal flick and the new page then loads with a very fast side-to-side fade that, unlike the Kindle reader, is a bit confusing. While reading a book you can look at the Table of Contents anytime, you can search for text and set what page to start the search on, you can invert the display so that you have white text on a black background (which can come in handy when you read in the dark), you can have the text scroll downward automatically, you can pick from eight fonts, six font sizes, four line spacings, six margin settings, and you can set justification on or off.
I am not quite sure why the B&N eReader gets only a 2-star rating as the reader worked just fine for me, but the weird way it flicks pages and having to enter a credit card number as an unlock code means it's no more than a 3-star in my book. The Kindle app remains the champ on my iPhone.
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