1. Chart.js is a JavaScript library that allows easy creation of data visualizations using simple configurations and options. It provides flexible and responsive charts that can be customized with various styling options. On the other hand, three.js is a powerful 3D rendering library that enables the creation and manipulation of 3D objects, scenes, and animations in a web browser.

2. Chart.js is primarily used for creating 2D charts and graphs, such as bar charts, line charts, pie charts, etc. It focuses on displaying data in a visually appealing and meaningful way, providing options for interaction and data exploration. However, three.js is specifically designed for creating 3D visualizations, including complex scenes, virtual reality experiences, simulations, and more. It offers a wide range of capabilities for working with three-dimensional space and geometry.

3. Chart.js is more suitable for applications that require data analysis and presentation, such as business intelligence dashboards or data visualization tools. It provides a simple and intuitive API for creating basic to moderately complex charts. Conversely, three.js is better suited for projects that involve creating immersive and interactive 3D experiences, such as games, architectural visualizations, or virtual reality applications. It requires a deeper understanding of 3D concepts and programming to utilize its full potential.

4. With Chart.js, the main focus is on the visualization of data, providing options for styling, labeling, and annotating the charts. It offers various chart types and supports multiple datasets, making it suitable for representing various types of data. In contrast, three.js focuses on the creation and manipulation of 3D objects and scenes, providing extensive capabilities for handling textures, lighting, materials, cameras, and animations. It allows for more complex and dynamic visualizations in a three-dimensional space.

5. Chart.js provides extensive documentation and examples to help users get started quickly and easily. It has a vibrant community of users and developers, ensuring a wide range of resources and support. On the other hand, three.js also offers comprehensive documentation and examples, but its learning curve can be steeper due to the complexity of 3D concepts and techniques. It may require more time and effort to fully master and exploit its advanced features.

6. Chart.js is generally lighter in terms of file size and resource usage, making it more suitable for web pages that require fast loading times and minimal performance impact. It is designed to work well on both desktop and mobile devices, providing responsive and scalable charts. Conversely, three.js tends to be heavier in terms of file size and resource requirements, as it deals with more complex rendering and computations. It may not be as suitable for low-end or mobile devices with limited processing power.

In summary, Chart.js is a lightweight JavaScript library for creating customizable 2D charts, while three.js is a powerful 3D rendering library for creating immersive and interactive 3D visualizations. Chart.js focuses on data visualization and presentation, while three.js specializes in 3D object creation, scenes, and animations. Chart.js is suitable for data analysis and business intelligence applications, while three.js is ideal for projects involving 3D experiences, games, and simulations.