Angular is a framework, which means you must commit to building the entirety of your application using the framework. As demonstrated when the Angular team rewrote Angular, changing a framework requires rewriting the entire application.

On the other hand, React and Vue.js are libraries, which means you can add them to your project and use them whenever is appropriate for you. You can also add additional libraries (for example, routers, state management) that will work with React/Vue.js.

Therefore, in terms of flexibility, React and Vue.js are the winners here.