ExtJs. / ReactJs.

Ext JS:

1. Framework vs. Library: Ext JS is a comprehensive JavaScript framework, while React is a library for building user interfaces.
2. Maturity and Legacy: Ext JS has been around for a longer time and has a more extensive codebase. It was initially released in 2007 and provides a rich set of UI components and features out of the box.
3. Component Set: Ext JS comes with an extensive set of pre-built, feature-rich UI components, making it well-suited for enterprise-level applications that require a lot of complex interactions and data visualization.
4. Complexity: Due to its comprehensive nature, Ext JS applications can be relatively complex and might take more time to learn and master compared to React.

React JS:

1. Virtual DOM: React is known for its Virtual DOM, which improves performance by minimizing actual DOM manipulations. It efficiently updates only the parts of the DOM that have changed.
2. Component-Based: React follows a component-based architecture, where the user interface is broken down into reusable components. This modularity makes it easier to manage and maintain large-scale applications.
3. Community and Ecosystem: React has a massive and active community with a vast ecosystem of third-party libraries and tools, making it easier to find solutions to common problems and extend functionality.
4. Learning Curve: React is relatively easier to learn compared to Ext JS, especially for developers familiar with JavaScript and front-end development.
5. UI Component Libraries: While React itself provides basic building blocks for UI components, additional libraries like Material-UI, Ant Design, and others can be used to create more elaborate and visually appealing interfaces.

Choosing between Ext JS and React JS depends on the specific requirements of your project:

• If you are working on a large enterprise application with complex UI requirements, Ext JS might be a good fit, as it provides a comprehensive set of components and features.
• If you are building a modern web application with a focus on modularity, performance, and a vibrant community, React JS would be a more popular choice.

Remember that technology landscapes change rapidly, so I recommend checking for the latest updates and trends before making a decision.