React is a library, not a framework. This means that it provides a set of tools for building user interfaces, but it doesn't enforce any particular structure or architecture. React allows developers to create components that can be reused across an application, making it ideal for building scalable and modular applications. React puts a big focus on composability within its structure, meaning you can easily take different components and combine them. Reducing coupling between components means they can be composed with a multitude of other components, which adds great flexibility to the way you build applications.
Angular, on the other hand, is a full-fledged framework that provides a complete set of tools for building web applications. Angular enforces a strict architecture, using a component-based structure and a hierarchy of services and directives.
While I only have a little experience working with Angular, back when Angular 1 was the latest version, I enjoyed having a full architecture that was pre-defined and needed no thought or consideration. An issue that often arises with React is determining a file structure and hierarchy that works for the application and for the team using it!
Angular has a steeper learning curve, with a lot of concepts to understand, such as dependency injection and modules. However, Angular provides a lot of built-in functionality that can save developers time and effort once they become familiar with the framework. Angular, in many ways, reminds me of Rails. There is a lot of convention within an Angular project that can seem somehow mysterious at the beginning, and definitely makes learning the framework more challenging, but they can be leveraged later on once you gain some familiarity.
React is known for its performance, thanks to its use of a virtual DOM. This allows React to efficiently update the user interface by only re-rendering the parts of the page that have changed. React is also lightweight, which means it loads quickly and doesn't slow down the user experience. With the emergence of frameworks like Next and Gatsby, server-side rendering and static site generation allow you to speed up the performance even further by rendering the HTML for the pages either at build time or on the server at request time.
Angular is also fast, but it's a heavier framework than React. This means that it can take longer to load and may not be as performant on slower devices or networks, although server-side rendering with Angular Universal has helped to bridge the gap with React and make Angular applications much more performant.
React has a large and active community, with many developers contributing to the library and creating third-party packages and plugins. React is also used by many large companies, such as Facebook and Netflix, which means it's well-supported and constantly evolving.
Angular also has a large community and ecosystem, with many developers contributing to the framework and creating plugins and modules. Angular is also backed by Google, which means it has the resources to continue to evolve and improve.
Choosing between React and Angular depends on a variety of factors, including the size and complexity of your application, your team's experience and preferences, and your performance and scalability requirements. While React is ideal for building scalable and modular applications quickly and efficiently, Angular provides a complete set of tools for building complex applications that require strict architecture and structure. Ultimately, the decision comes down to your specific needs and goals.