You in particular? No, I cannot answer that question. I don't believe there is a single language which all programmers should be using.

In general? It is a strongly typed functional language with excellent type inference that isn't lazy and support imperative programming. I think (and this is opinion) that it much easier to reason about an program written idiomatically in a dialect of ML (such as F#) than one written in idiomatic Haskell, basically just due to the lack of laziness. I also think I prefer Haskell to the ML variants, but I also found the hump which one has to get over in order to be productive significantly lower.