Kotlin. Learning curve is gentle, reduced boilerplate, aggressive null handling, first class language support in IDEA and interoperability with Java codebase.
Kotlin for me too. It’s like the pinched the cool bits from other languages to boost java. Plus the power of java ecosystem. The tooling is amazing because obviously it’s Jetbrains’ baby. Gradle are on board as are the android team. Spring boot lot are going for it. It stands a good chance of getting a lot more mindshare than it has currently