I wanted to share my experience with selecting a mobile backend for my app. I used to run my applications (I have several in the app store(s)) on Parse and was pretty happy with the backend until Facebook decided to shut down the service. After that I have evaluated all listed options and was not happy with any of them for various reasons. Firebase was not a good fit because the of their approach with JSON document being a database - I did a stress test with million nodes in the tree and the service was not performing well. AWS and Appery are quite complex and become expensive very quickly while Azure and built.io are quite limited in the capabilities. Kinvey is both limited and super expensive once you start doing something more serious in the app. In the end I chose Backendless for my backend. The service has native SDKs for all major mobile and web platforms. The usability and developer experience is by far the best I have seen. The service has an extremely flexible server-side code model where I can deploy Java and JS server-side code to override default handling of the API and to create my own API services. My apps leverage social (Facebook, Twitter, Google) login, geolocation, file upload/download, push notifications (iOS, Android) and of course data persistence, which has really awesome support for complex relations. Check it out if you are looking for a flexible and very reasonably priced backend.