I’m glad you posted this thread as I want to evaluate what to use with my first Phoenix app too.
For Elixir/Phoenix projects I am leaning towards Elm - I really like the speed, stability, that it is functional, and that it is not javascript (I am not a fan of JS).
There is also an Opal Phoenix wrapper if you like Ruby.
For Ruby projects I would look at one of the front end frameworks, of which there are now many: Volt (which is an isomorphic front and back end framework) Clearwater, Inesita or just plain Opal. There is also React.rb a Ruby wrapper for React.
