Here are images of what Oyster's interface looks like. I like that they have more fonts options including textured background. They also have a reading time prediction like Kindle. I also like that you change pages by either side taps or vertical scrolling.
https://www.oysterbooks.com/features
https://itunes.apple.com/us/app/oyst...672803850?mt=8
Here are some links for Scribd. One extra feature they have compared to Oyster is a search within a book.
http://support.scribd.com/entries/63...on-Scribd-com-
https://itunes.apple.com/us/app/scri...542557212?mt=8