Here, the first question you really need to answer is which platform would opt to design your app. Answering this question is incredibly important since it can directly affect the potential your app will have in terms of gaining monetary returns since every platform has an entirely different ong audiences.
Developers conventionally earn well in the app domain since there is a consistent demand for apps to be developed. Having said that, opting to become a developer for Android apps will allow you to potentially earn more since the average salary for Android developers is around $97,600. The higher earning potential here is quite understandable since Android has a lot more users and higher market penetration than iOS.
But don’t think that iOS developers are not adequately compensated. A mid-tier iOS developer can earn a per annum income of around $96,600.