Hi,
None is better, they're just different, React being client side and F3 being server side routing. It will depend on what or how you want it.
If you're using React just for simple components you may be able to do without React routing and just loading your react components through regular script tags that are loaded through your F3 routes.
Also, even if you use a more complex React app with routing, you'll probably also have to setup routing on F3 in order to use it as an API endpoint for React to fetch or post data using (for example) ReST or GraphQL.
So, for example, a /users/list route in React may do an GET request to F3 at /users in order to fetch all users from your backend.
Or a /users/create route on React may submit a POST request to F3 at /users in order to save the user to the database, etc.
Good luck.