GCloud, I'm a fan
I guess all the big cloud service companies offer the same thing. In one form or the other, but very similar. I decided to create an app using only GCloud for my back-end needs.
I built a NodeJS back-end in support of a mobile game which uses Unity as the game engine on the front end. I like to have the actual OS perform some of the heavy lifting instead of Unity itself.
My network calls take advantage of of retrofit and a more robust Serialization/Deserialization of objects returned from the server. I can offload background "jobs" that can be scheduled at any time. Not only when the app is run. This allows me to set up cool scenarios driven by the server.
I'm a fan. Very easy to set up. Creates extremely powerful, useful and affordable services to help your app achieve it potential.