It depends on your requirements. I have been building www.confluo.app, a social task assistant, in my part-time for about 2 years now. I wanted it:

1) to target both iOS and Android devices

2) to be real-time for social networking and collaborative tasks

3) available in both offline and online modes

4) to have no cost of developing and testing with small audience.

Turned out I could achieve all of the above using Flutter + Firebase (Auth & Firestore).