I think personally that your question is some strange. If you do a job because of future prospects you might find yourself some day in a sad position because you might not like your job and have wasted your life. If you like your job you will invest time and energy to achieve, if you don't like your job you won't. So what do you like? Musculoskeletal or Neuro? Neuro physios are rare. But it can be fascinating work. The same though can be said about musculoskeletal with all the developments.
Sorry not an answer, make up your own mind by doing what you really want because you love to do it at this moment not because a brilliant future prospect. Otherwise you won't be proud of yourself tomorrow.