IMO, it depends on your background. If you have a lot of functional programming experience in languages similar to Erlang, I'll say just go ahead with Erlang.
If you come from a more traditional language background, such as C, C++, c#, java, scala, ruby, python, js and others, especially ruby since elixir is very ruby-ish, Elixir is more approachable and I'll suggest that you go with it.
LFE - Lisp Flavoried Erlang - is also an option. Created by Robert Virding, one of the creators of Erlang, it is a Lisp-2 with full access to Erlang and the OTP.
Elixir is cool though too, and certainly is similar to Ruby.
If you come from a more traditional language background, such as C, C++, c#, java, scala, ruby, python, js and others, especially ruby since elixir is very ruby-ish, Elixir is more approachable and I'll suggest that you go with it.