Well, both MEAN and MERN are easy to learn. Both of the stacks require the knowledge of MongoDB and Node.js. The only difference is React & Angular.
I used to write Angular apps a few years back before I switched to React. For me, unidirectional data flow and reactive programming made more sense. It's true that React is the view, but if you understand Flux architecture and use React along with it, this can be a great combo. Angular 2 is still in beta. Although you can learn it, you will need a stable release to build a production ready app. If I were you, I would start learning React and then slowly get started with other parts in the stack. The community support is great and we are seeing more and more companies adopting React everyday.