I started using Phoenix for my most recent side project. So far, am really liking Elixir and everything that comes with it. Obviously, I am still learning, but the inclusion of the entire Erlang ecosystem is a big plus.

Will have to say that working with Elixir and Phoenix (so far) has been much more enjoyable than working with Rails.

I will say the only thing I really miss is extra tooling for debugging and so on, but I'm primarily a java developer, so I'm used to having all sorts of options at my fingertips for debugging.