I haven't ranked them, but I've provided some input on what formats they support here
on the wiki.
Right now I'm pretty tied to readMe as it is the only non-DRM ePub reader available (other thank Bookshelf) which supports a night view. I personally couldn't stand BookshelfLT because it put ads ON the book itself. readMe has some bugs so it's not the best thing since sliced bread, but it suffices for most purposes, and works with calibre.