Xamarin or Kotlin for Android development?

Well out of those options, I'd say Kotlin because you'd understand the Native Android APIs better than if you first used Xamarin

Xamarin is the best solution than kotlin or java android. because the c# compiler is full object-oriented compiler that supports by Microsoft the giant of software companies. in Xamarin you can easily programing as Native Android , Native IOS and Forms for both .For example you can use All Android APIs and IPhone SDKs by C# in Xamarin . Xamarin is future of Mobile programming.