I’m a huge advocate of Android. To date I’ve only built Android apps, largely because our iOS test device collection equates to exactly one rather old iPad (from 2013 possibly!), and also because I don’t want to start paying the annual license fee to publish to iOS until mobile apps are making a reasonable amount of revenue already.
But, despite my bias, I’m also of the opinion that iOS is where the money is.
Android has the market. It’s huge - I think I read somewhere that more Android devices sell every year than the entire number of iOS devices that have ever been produced. You can pick any free app and compare it’s Google Play store download count to an Apple store count and the Android count will be far higher. Look at any article that focuses on stats like this and you’ll wonder what the point in publishing outside of Android is.
But, if you look at the global distribution of Android sales, you then find that they have the market almost entirely because poorer countries buy vast quantities of cheap Android devices. These are people who can just about afford to have something nice, but not to also buy commercial games or apps for it. Additionaply they’re generally on older Android versions, and low range hardware.
iOS on the other hand, while having a smaller audience, tends to sell more to the west. Pretty much every iOS user is somebody who doesn’t think twice about paying for apps. Apps are almost expected to have a price, and because iOS devices are more of a standardised spec and the software is optimised specifically for that spec, if an app is in the store it’s pretty much guaranteed to work properly on the device the buyer is holding, so there’s no need to wait for something to have a reasonable following before trusting that you’re not about to buy something that’ll run poorly.
Looking at the bigger picture, it makes total sense to publish to iOS, and for iOS sales to out-earn Android sales. But if your app is free, it’ll probably get more downloads on Android. Just remember that most mobile ad networks seem to be priced around installs, not clicks, so a free app on Android running adverts that pay you when the user installs the advertisers app and earns them some money might not necessarily do any better than a paid app would, since your probably poor user still isn’t going to install the paid apps that you’re advertising.