Disclaimer: I work for Kinvey on their development team.
Kinvey[1] is another BaaS platform with a pricing model based on users instead of API calls. We also have quite a few integrations, including the ability to run code on a pre-save/post-save on a different server if you so desired.
At the end of the day, there are a bunch of decent choices out there, it all depends on what features and pricing fit your needs.
Well, if you are building a very simple system it's quite possible you don't need a backend at all. Our goal when designing the tool was to help people get an estimate of how much it does cost to build an app, hence we have some options that don't strictly point to backend features.
Kinvey[1] is another BaaS platform with a pricing model based on users instead of API calls. We also have quite a few integrations, including the ability to run code on a pre-save/post-save on a different server if you so desired.
At the end of the day, there are a bunch of decent choices out there, it all depends on what features and pricing fit your needs.
1: http://kinvey.com