Android takes longer to develop but has more market share.
iOS is easier to develop and users are willing to spend money.
>iOS is easier to develop
These are old myths. Yes, in some cases iOS has an easier time, in other cases, it's a PITA. Where you have IntelliJ editor and gradle build system on android, you have XCode and uhhhh whatever they call that system.
I find Android is easier to develop if you have general development skills/knowledge, while iOS requires more iOS specific skills and knowledge.
But, to get to your question, the answer is the most common one: it depends.
What is the app? Who is your target audience? Where is your target audience? What's your funding/features/monetisation/timeline like? Where are you located and where are you going to hire? Why not try Flutter?
Sometimes it might seem "Oh yeah iOS user spend more and is easier to develop" but then you end up on a wild goose chase for skilled iOS developers who won't turn your codebase into trash and then dealing with apple's ecosystem regarding testing, purchases, releasing and all that comes with it. But similar problems can come up with Android too so in the end it just really depends on the answer to above questions.
I guess it just depends on what phones you have handy to test!
I really like React Native, but it's not the right solution for everything. I've heard Flutter is pretty nice too, so consider your options for cross platform development if it's a good fit for your app. That being said, neither is a very good for for complex apps like games.
If I have to make a separate app for both platforms, I'd do whatever I use for my personal device first so I can make sure I can easily test it in real world usage. Once the idea is proven and you have real users, expand to the other platform and step up your marketing game.
Depends on the user base as well. Which users are likely to use the app and you're able to retain easily.
Another factor is how well you / developer knows the platform. For example, if you have always been writing React Native apps, then you can do RN but focus only either iOS / Android app. That way you can give one platform your 100% and then quickly launch to the other platform with lesser work.
If it's a paid app aimed at a "professional" market I'd go for ios as, if I recall correctly, ios users are more inclined to spend money on an app than android ones.
Considering the demographics of India, and our limited development team (a single founder), we decided to focus our efforts on Android.