Node.js or Erlang

Question

I really like these tools when it comes to the concurrency level it can handle.

Erlang/OTP looks like much more stable solution but requires much more learning and a lot

Answer 1

I would give Erlang a try. Even though it will be a steeper learning curve, you will get more out of it since you will be learning a functional programming language. Also, since Erlang is specifically designed to create reliable, highly concurrent systems, you will learn plenty about creating highly scalable services at the same time.