Common benefits that they both share is the ease of implementation and flexibility. But there are certain capabilities that distinguish them from each other. React.JS is a library that can be integrated into your code whereas Angular.JS is a giant in itself that inculcates the complete framework and implementation details. As compared to Angular.JS, React.JS is easier to learn and faster to implement. Due to its good support for mobile applications, React.JS is the most opted-for JavaScript library for the Mobile App Development
Taking into account the mobile application development, using the MEAN approach includes availing the strong capabilities of the Ionic framework whereas the implementation of MERN is best benefited by the use of React Native.
The selection of MEAN/MERN stack wholly depends upon the development and functional requirement of the system to be developed. Choosing either would provide you with proficient software according to their capabilities.