If you are trying your hands on android development go with Dart because it gives you cross platform flexibility.
Code ones run everywhere.
Dart is very simple to start with and learning curve is easy. Lots of library are available to help faster development curve and look is very native like as it provides 60fps performance.
Flutter is an SDK to build cross-platform mobile apps Android Studio is an IDE focused on mobile app development
There is no "OR" option here. You can use Flutter and Android Studio both in a project - these 2 exist for different purposes and do not overlap, hence no competition.