It doesn't matter Just pick one and stick with it for a while. Learn some stuff, make some cool things and either keep going with that language or move on to another one.
With respect to learning concurrent programming, either will be fine. The key here is that you will be learning something new and unless there's a job opening that you are trying to get hired for that uses Erlang specifically, it really doesn't matter. Plus, even if that opening did require Erlang, you would still likely have a good chance if you knew Scala really well.
Just think, all of the time you have spent trying to pick a new language could have been better spent if you just picked one and already started learning it by now.
