I haven't spent much time with calibre-web in a long time but can confidently say BookOrbit blows it out of the water in terms of functionality. I love that I can have one app that handles books and audiobooks. The ecosystem of apps that work with it is growing quick too, Apogee for iOS being a standout for me. They recently added readaloud support (like Amazon Whispersync or Storyteller) natively in the app, which I've never seen done before.

I have no relation to BookOrbit except I'm a very happy user.