I am now building a React Native app, and I don't know what to choose for my backend between AWS Amplify and Firebase. Which one fits more with react native?
Both AWS amplify and Google Firebase fit perfectly with RN. Both are useful for MVP development, where you need to quickly and cheaply(?) test a market idea, as by using one of these, you do not need a bunch of backend developers and DevOps people. Even a serious project can be completed by single freelancers, like I did for my current client. Let's try to compare them quickly...
Firebase : It's a feature-rich platform with all tools you need to make you up and running at a very affordable cost. It's easy to use and doesn’t have a high learning curve. It's for me best suited for small and medium-sized projects, as costs may become really prohibitive for projects with a huge amount of data transactions.
Amplify: A little bit more "advanced" platform that lets you leverage the power of AWS (as it is using CloudFormation (Infrastructure-as-a-code) behind the scenes, you can always add more resources). It offers GraphQL capabilities, that Firebase doesn't. I think it's more suitable for big projects as you can fine-tune the pricing depending on your needs.
FIrebase offers many services that do not exist in AWS Amplify (e.g. Crashlytics, Cloud Messaging, Analytics), so even if you go with Amplify as the main backend, there is a chance you will add Firebase into your project too for some of its essential features. And yes, both can live together in the same project, as they can be complementary.
Conclusion: if you're starting a project from scratch, and you're not already comfortable with AWS world, then go with Firebase :)
