The best tool to use is the one you already know. This is what drove us to use Rails and PostgreSQL to power our backend. Rails is already optimized for web API development, which is perfect for our mobile apps. Active Record and the suite of other Rails tools lets us prototype and push production-grade code very fast.

Since Rails has existed for quite a long time, its ecosystem has had enough time to mature and provide a lot of support. This gives us a very solid foundation on which apps were battle-tested in production that we can rely on. This is crucial for a small team — we generally do not have the bandwidth to investigate weird issues with new frameworks nobody has ever seen before.