[wirddin]

Adding to lm28469's answer:

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.