Kotlin is more functional than Java, due to its extra features. It is also easier to work with multithreading apps due to Kotlin's Coroutines tool. Yet, the language compiles and executes a little slower than Java, which is mainly due to the extensive number of features.

Kotlin is the preferred language for Android application development in 2021. Both Java and Kotlin can be used to build performant, useful applications, but Google's libraries, tooling, documentation, and learning resources continue to embrace a Kotlin-first approach; making it the better language for Android today.