If you want to be a better developer, learn one of the functional languages (Haskell, Erlang, F#/Ocaml, Scala, etc.).
If you want a better paid job, learn Java or C#. It doesn't really matter which one as they're close enough that when you learn one of them then the other can easily be picked up. Though you might want to look closely at the pay rates (here in London, Java developers tend to get ~10k more than C# developers)
Couldn't Scala bring you closer to Java? It's the only recommendation which could be better all around for a developer (I'm not a scala Dev).
It could, though last time I played with Scala there was a lot of doing things its own way - like having its own collection class hierarchy. Not a big deal but it did annoy me a bit.
Another option would be F#, as that sits on top of .net. Personally, I found F# a lot easier to pick up and it felt a lot closer to the rest of .net than Scala did to Java.
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