I would say it depends on you :-), the amount of time you are dedicating to this learning and what is the goal of your learning.
It's easier to start learning a language in your current environment, for example learning Scala if you are a Java developer or learning F# (OCaml-like) if you are a c#.
If you wanna master functional programming thinking, maybe Haskell or Idris are the best school (language fully based in the concept of function as mathematical entity, pure as they don't have side effects).
I will love to learn Elixir or Erlang but more for the beauty of OTP and the elegance of the actor model than the languages themself.
Clojure is an interesting language (lisp family) and JVM world, but here you are more in the dynamic world (vs strong type system as Haskell or Idris), so it may be an option if you are interested by an elegant implementation of a dynamic language.
You can add many other interesting languages to the list (like Elm-lang which is a very intersting option if you want to do web development using a functional language)
So every language have his pros and cons, define your goal and the amount of time you will dedicate for this learning, if you can experience different language that will be even better.
Cheers