It depends on what is the purpose of your app development. Do you want to make one app that shares the codebase for both iOS and Android? If yes, then Dart is the way to go. Does your app include interacting with hardware features like camera, Bluetooth, if yes, then go for native Android for better performance? Dart is good for simpler UI apps where you just do basic crud operations over the network and show data but if you need richer UI experience go with native.

I assume that you mean Flutter by Dart. I have over 6 years experience programming in Android SDK, but about 1,5 month in Flutter. So far I think that Flutter is the future for mobile development. Flutter SDK is much better designed. Ecosystem of libraries seems having much higher quality. I would even say that android opensource libs are having really poor quality. Many times I am wondering how can garbage like that have so many stars at GitHub. Android SDK is hard to compose so you reinvent even basic things on and on, which is totally different story at Flutter. Lolcycle? Both are having good documentation. I quess apps in Flutter can be done in 1/3 of time compared to develop AndroidSDK and iOS, its design is that much better and contemporary. As of language comparison - Kotlin is better, but the difference is not that important. Go from one language to other is no problem. Dart is being updated with new features.