If you work in a .Net environment and want to explore the possibility of using functional programming on the job, F# is definitely a natural way to go.

Depending on how much autonomy you have at work, Haskell is a reasonable language for getting "real work" done. The technology is ready to do the job: as with any language selection discussion, the issue is more about workplace culture (maintenance plans, hiring, etc).

In terms of advanced types, my understanding is that F# is playing catch-up to Haskell, but that's not really a slight against F#. I happen to prefer Haskell, but it's not obvious to me that a person who knows both languages would agree with me.

So the answer your question, or more precisely to not answer it, I think you'll find either language rewarding. If you think F# might be more useful at work, that's definitely worth considering. If you want to see the state of the art in (well supported) statically typed functional programming, Haskell is a strong contender. Regardless of which you decide to look at, the skills will translate fairly well if you later go to look at the other.