I can't speak about experiences with Ruby/Rails since I don't use that stack but I can give you advice about both Scala and Elixir. I used to be a Java program

I can't speak about experiences with Ruby/Rails since I don't use that stack but I can give you advice about both Scala and Elixir. I used to be a Java programmer and fell in love with Scala and functional programming. Scala helped me do things that I couldn't do so easily in Java in a more explicit way. However, I found doing web development with Scala to be more cumbersome than helpful but was still a great learning experience for FP in general. Since late 2015, I've been all-in on Elixir. Elixir does everything I wanted to Scala, specifically pattern matching everywhere and how powerful it is. Since Elixir uses BEAM, it's incredibly lightweight but can scale without any configuration. The community around Elixir is fantastic and helpful and everyone is growing together. Brian Cardarella (well known in the Elixir community) gave a conference talk at Rails Conf about switching from Rails to Phoenix (Elixir's goto for web) and that may be a good start to empower you to make a decision: https://www.youtube.com/watch?v=OxhTQdcieQE https://www.youtube.com/watch?v=OxhTQdcieQE. A great resource for learning Elixir if you choose that route is Programming Elixir 1.2 by Dave Thomas. It's a great book for beginners and can help with you understand Elixir semantics and functional programming.