I'll just add two points to Joshua David's answer:
Meteor, since it's a single framework, offers a more streamlined, coherent development workflow. The Meteor CLI does most of the heavy lifting for you, from dependencies like Node/Mongo, to package management, to automatically watch and reload during development. With MEAN there's going to be more manual plumbing required.
Meteor's core value is the simplest data synchronization between the server and the client (realtime is just a side benefit). And it does not require you to use the built-in Blaze rendering engine. In fact we are moving toward a frontend-agnostic platform. If you want, you can easily use Angular with Meteor, and we have an official tutorial for that. The best part is, with Meteor you get the realtime magic and optimistic UI updates in Angular as well! In the upcoming 1.2 release we are going to offer official support for React, and will continue to work on making it easier to choose other frontend frameworks in the future.