Like most things in programming, 'it depends'! What's your background? If it's in a more interpreted language like Ruby or Python, learning Elixir instead might be a good idea. If you want something that's going to be more approachable, it also might be a better idea. Are you going to do web development, and want to use a more conventions-over-configuration type of framework? Do Elixir with the Phoenix framework.
If you already enjoy Erlang though? Don't get discouraged just because something is built on top of it- keep going! Elixir will be there regardless, and might even be easier to learn when you understand what it's built on.
Elixir is a different syntax and standard library on top of the Erlang VM (BEAM) and OTP, the distributed/HA magic written in Erlang, that Erlang (ecosystem) gets a lot of its praise for.
Ultimately you'll need to know Erlang (language) anyway if you want to use some external libraries that aren't in Elixir natively. IMO, Elixir as a language is not too different from Erlang, other than syntax.
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 already enjoy Erlang though? Don't get discouraged just because something is built on top of it- keep going! Elixir will be there regardless, and might even be easier to learn when you understand what it's built on.