The first one-million dollar question that comes to every Android developer while starting a new projec t would be
There are tons of articles out there for the reasons of picking up Kotlin. Here is one of it.
Personally, I would prefer to have Kotlin.
Kotlin is interchangeable with Java, cleaner, more readable and “null- safety” feature of Kotlin helps developer to think thoroughly before hitting NPE (Null Pointer Exception).
Furthermore, Android announced to support Kotlin since May 2017!
We can also see the effort of Android team on improving Kotlin Development in Android Studio!
Not only that, Android team has actually used Kotlin while announcing new features in their latest video!
Kotlin tutorials can be found easily online!
Since Kotlin is interchangeable with Java, developers can continue to proceed with Java anytime.
P/S: * Developer can make a decision based on project timeline, familiarity to the language, further technical supports from third party (eg: client SDK)