I would use Java 7 rather than Scala in production environment. There are different reasons, some actually concern language features but one of the biggest is IntelliJ's capability as Java IDE. It blows away all of the other alternatives as efficient way of creating readable code that is breeze to refactor. Even though Java lacks features that make life easier, the lack of features is important, too. And as a former Scala enthusiast (when it was not so hot), I just dislike Scala's monstrosity. I have high hopes for Kotlin because it has some advanced stuff that have been clearly included by the experience of using Scala. And it in all likelihood will have very good IntelliJ interop, because JetBrains.
I don't get it why people fuzz over languages without a context of tools.
I don't get it why people fuzz over languages without a context of tools.