I prefer 'BookShelf'. Its created by Zach who made the first Books application on the iPhone. It supports multiple formats and it supports Mobi-pocket format, which is all I wanted
Its $10, but for a person who reads a lot of books on the go, its totally worth it. Sync'd through your computer and also access to free public domain books. You can change the fonts, backgrounds etc. Tilt and autoscroll supported. There is support for Bookmarks etc.