I've always liked OCaml and with Facebook putting some real momentum behind it and the OCaml/JS story getting better and better all the time I'd say now is a go

I've always liked OCaml and with Facebook putting some real momentum behind it and the OCaml/JS story getting better and better all the time I'd say now is a good time to pick it up. It's more pragmatic than Haskell, simpler than Scala, and not tied to the .Net ecosystem like F#.