Well in reality I choose Scala, largely because it has a level of maturity and ecosystem support (both libraries and other tools) that neither Ceylon nor Kotlin can match. But I'd use Ceylon rather than Kotlin because I think it's a much better designed actual language (see cousin post for examples). I personally dislike IDEA (prefer Eclipse), and I don't think Kotlin actually has any better Java or android interop than Ceylon (or Scala), they just make more of a fuss about it in their marketing.