I agree with iBooks, reading a book with the Kindle app now (because the book wasn't available in iBooks) and it really pales by comparison. Although it does have one neat feature, you can run it with white text on a black background which is cool if you don't want to be staring at the bright white screen at night.
You can do this with iBooks also, you just have to change the whole iPad setting to White on Black . You can even set up a triple click on home button to go to white on black. Look under Settings/General/Accessibility
That is great info, and iBooks is truly the best E-reader I've used!