Both MEAN stack and Full Stack development are very good. MEAN Stack is by definition is Full stack but in MEAN stack you just work with JavaScript Technologies like MongoDB, Angular, ExpressJS, and NodeJS. A full-stack developer can choose any technologies for their web application like React for front end and Django for the backend. So if you wish to learn and use the only JavaScript for your web application then you can use MEAN stack, and if you wish to learn different languages and combine them together then you can learn Full-Stack.
You can also read this blog that explains what MEAN stack is.
You can also get started with MEAN stack by learning individual technologies, like:
If you wish to learn MongoDB you can do this end to end certification course on MongoDB.
Also you can learn Angular by doing this Angular course.