Haskell is worth learning because a lot of the work done in FRP has been done in a Haskell mindset. Flapjax, Fran, reactive-banana, Elm---all are written in Haskell or trace significant ancestry therefrom.

Clojure is worth learning because, well, it's the future, but also because the community seems to be bent on finding actual application for lofty CS concepts. If you want to use facebook's React, you can use JS, coffescript, facebook's "JSX" compiler, or clojurescript. I'd argue that clojurescript is the most pleasant option.

If you want to learn about FRP inside and out, Haskell. If you want to write something cool and reactive, Clojure.

(Other names to look at if you go clojure: Shafty, Javelin, Lamina, core.asynchronous)