I am not advocating anything in particular as I am in the process of choosing the next language to learn. That said, I have watched some talks by Cheng Lou and some others about ReasonML.

Elm is just "Elm"... that isn't a bad thing and it seems like it is more mature at the moment.

ReasonML is Ocaml that plays nice on any screen anywhere thanks to Bucklescript. It also plays nice as a systems language. That is, unikernels... I am not even sure what they are, but they sound awesome and I want that.