Startups should prioritize experience, versatility, and a proven track record when choosing a React Native app development company. Look for a team that has successfully launched cross-platform apps across industries and can showcase real case studies. The company should be adept in optimizing code for both iOS and Android, following best UI/UX practices, and offering post-launch support. Clear communication, agile development processes, and the ability to scale as your startup grows are also key indicators of a reliable partner for long-term success.