I think React Native is the most "mainstream" which has some benefits. Dart is a fresh take which certainly can learn from RN issues and attracts folks who don't like coding in JS (which might be a more "advanced" crowd).
I don't know much about the Ionic tech or community but it strikes me as a pretty good tool which hasn't always found the consistent "why you should use this" message.
Ionic's pitch as always been pretty simple: want to use standard web development tools/technology/libraries for mobile (and PWA/Desktop)? Ionic is a great fit.
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