Hi there. In response to your question, both of the fields are really enterprising. Candidate wise it should come down to what you're interested in following your passion as and also as it's the master degree, you can use your knowledge of the bachelors degree to know whether you are really interested in one of the two subjects, usually an undergraduate degree can act as a motivation to go for your masters as you feel comfortable around a certain discipline and want to work in its respective fields. Hence you can use these pointers to make a decision.

Hope this answer helps; best wishes