I'd imagine having Jetbrains behind Kotlin means much better tooling, which is likely to be more important for a lot of people than language features like ADTs.
to be fair, I presented that before Kotlin hit 1.0. A few things that I liked are no more (like the @-less syntax for annotations). But all in all I believe it is still a good commentary.
https://speakerdeck.com/evacchi/kotlin-and-ceylon-modern-pro...
I can't say I've used Ceylon much but I think Kotlin's syntax is much nicer and it's much easier to approach than Scala.