I work with both native iOS and React Native on daily basis. Both had their own (dis)advantages and it's hard to have a definite answer on which is better. It all depends on the nature of the app you want to build, your budget and trade-offs you are willing to take. RN is moving fast and has improved a lot in the recent months but still has some pain points:

- If you want to build a chat app, forget about well working sticky text input. (https://github.com/facebook/react-native/issues/371)

- All the dev time you have saved with hot reloading will be lost if you hit the infamous 4968 (https://github.com/facebook/react-native/issues/4968)

- Multithreading, but that has been covered in other comments. If you're obsessed about buttery smooth UI you'll have some unpleasant time.

Also :

- I find RN's ecosystem feeble and don't trust packages. Triple check everything you run npm install on.

- Using solely RN/JS is not an excuse to completely avoid learning native development. It bites in the future.

+ ScrollViews are great.

+ Build times are shorter, you get quicker feedback especially for UI small modifications.

+ I really enjoy working with RN's Animated API.