If you're talking about tool availability and production readiness then I think Scala has the advantage over Kotlin. By the time Kotlin reaches a similar level of maturity, how many features will it have that haven't found their way into Java?

(I don't think Scala's a thousand-year language, but I think Kotlin drops too much of what makes it good; I'd look to the likes of Ermine as a potential future replacement. But more to the point, Scala is production-ready today - I know because I use it in production)