Choosing a cross-platform framework is one of the first big technical decisions a startup makes. Here's how Flutter and React Native compare in practice, based on 8+ years of shipping both.
Performance
Flutter compiles to native ARM code and renders its own UI with Skia, which tends to give it the edge in animation-heavy apps. React Native (with the new architecture) has closed much of this gap, but Flutter still edges ahead for consistently smooth 60fps+ experiences.
Developer speed
If your team already knows React, React Native gets you to a working app faster. If you're starting fresh, Flutter's single codebase and strong tooling (hot reload, widget inspector) make it very productive too.
My recommendation
For most new products I recommend Flutter, unless the team is already deep in the React ecosystem or needs very tight integration with existing React Native modules.