This is a matter of personal opinion. If you just want to learn how to read and write at a high level, distance education could technically work (I'm not a huge fan to be honest, but that's just me).
However, you are talking about learning to become a teacher. This goes beyond knowledge of words and grammar. One of the impost important parts about effective language teaching is how you engage students, organize an effective lesson, and manage your classroom, often adapting in the moment as needed. Many teaching models, especially for teaching languages, are moving toward student-centered, communicative approaches. I agree with that trend. The traditional approach of having students diagram sentences only gets them so far. I have seen how effective the communicative approach can be.
It takes skill and discipline as a teacher to have the students do most of the talking in a class (and to make that talking productive and meaningful). The best way to learn how to do this is to shadow other teachers and to practice in your own classes and in real settings. A distance education program might be able to show you videos of how to do this, but you won't be able to practice in a real setting and receive feedback to improve your skills.
I am not claiming that my measly 30-day TEFL degree comes close to an MA, but just to give an scaled-down example, of the 150 hours I spent in that course, the most meaningful were clearly the 10 hours of instruction and feedback from experienced teachers. When taking teaching jobs abroad, I found it very useful to watch other teachers in their classrooms. Sometimes the teachers were very skilled and I learned a lot. Other times I saw teachers who, in my opinion, were not facilitating language learning very well, but those experiences also taught me what not to do.
Bottom line: For a profession based in personal communication, I suggest learning in a context of personal communication.
Some people will disagree with me (and of course, please think about all of the pros and cons and consult others in your decision process), but that is where I stand.
- For Teachers