These frameworks are very limiting comparing to developing in Java. They might be easier to use (I don't know about that) but you would find yourself resorting to Java for the more complex stuff.

Can you come up with one thing that you can't do with Xamarin (C#) that you can do in Java (Android)? It's most certainly not 'very limited', I have no idea where you got that information.

You have the Xamarin extra payload and need to have someone write .NET bindings for the Android APIs.

But it is certainly a good way to write portable software across all mobile platforms.

This http://kotlin.jetbrains.org/ is the best language for Android development.

I think you should motivate 'best' :).

In general, Kotlin is a good candidate for the next Java. It removes a lot of boilerplate from Java and makes it more powerful (e.g. through extension methods), without becoming an enormous language such as Scala. It is a predictable language for anyone coming from Java.

Kotlin's largest competitor is Java itself. Java 8 does provide a lot of the advantages that Kotlin had (e.g. closures).

Java 8 unfortunately does not have closures

http://stackoverflow.com/questions/17204279/does-java-8-supp...

By that standard Haskell doesn't have closures either.

A closure is a function that uses free variables in its definition. And Java 8 closures fulfil that definition.