MVVM separates your view (i.e. Activity s and Fragment s) from your business logic. MVVM is enough for small projects, but when your codebase becomes huge, your ViewModel s start bloating. Separating responsibilities becomes hard. MVVM with Clean Architecture is pretty good in such cases.

What architecture does Android use?

Linux kernel.

Android uses a version of the Linux kernel with a few special additions such as Low Memory Killer (a memory management system that is more aggressive in preserving memory), wake locks (a PowerManager system service), the Binder IPC driver, and other features important for a mobile embedded platform.

Which design pattern is best for Android?

Model View Controller or MVC is an Architectural Design pattern this is used to write an organised code for Android applications.