For me, I think the overall best reading app is Mantano (the paid version) because it renders most of the CSS more faithfully than the other reading programs. It also has a lot of other options and features so you can tailor the interface to just how you like it.
My only gripe is that it can't display covers with very large pixel dimensions but they say they will try to fix this. It would also be nice if there were a free way to sync reading position like Moon+ has. But those are minor niggles, and overall Mantano is my favorite.