1. DOM Manipulation and Rendering: Marionette is primarily focused on providing enhanced structure and organization to Backbone.js applications by adding features like regions, layouts, and views. It provides a higher level of abstraction for managing complex UI structures. On the other hand, React is a JavaScript library that focuses on efficiently updating and rendering components based on changes in data. It achieves this by using a virtual DOM to minimize changes in the actual browser DOM, resulting in faster rendering and better performance.

2. Component-Based Architecture: React is known for its component-based architecture, where the UI is divided into smaller reusable components. Each component manages its own state, and React efficiently updates and renders only the components that have changed. Marionette, while providing some similar concepts, is more focused on application structure and managing the relationships between views rather than component-based development. Components in Marionette are represented as views and managed through Marionette's view hierarchy.

3. One-Way Data Flow: React follows a one-way data flow, where data flows from parent components to child components through props. Child components cannot directly modify the data passed to them; instead, they raise events or callbacks to the parent components to update the state. On the other hand, Marionette does not enforce a specific data flow pattern and allows more flexibility in data manipulation and sharing between views.

4. Virtual DOM vs. Backbone Models: React uses a virtual DOM to efficiently update and render components by comparing the virtual DOM with the actual browser DOM, minimizing manipulation of the actual DOM. On the other hand, Marionette uses Backbone models and collections to represent and manipulate data. While Marionette provides abstractions for handling events and data binding, it does not have a built-in virtual DOM like React.

5. Community and Ecosystem: React has a large and vibrant community with extensive support, resources, and third-party libraries available. It is widely adopted and used by many companies and developers. Marionette, while also having a supportive community, has a smaller user base compared to React. This can affect the availability of resources, documentation, and community support.

6. Learning Curve and Complexity: React has a relatively steeper learning curve compared to Marionette, especially for developers who are new to component-based development or virtual DOM concepts. Marionette, being built on Backbone.js, can be easier to grasp for developers already familiar with Backbone or similar frameworks.

In summary, key differences between Marionette and React include their approach to DOM manipulation and rendering, component-based architecture, data flow patterns, the presence of a virtual DOM, community and ecosystem support, and the learning curve and complexity associated with each framework.