I think you should study what you like best, not what is marketable in the workplace, remember engineering is hard so at some point you will get to a point where you will ask yourself "what am I doing studying this" and if it is something you like then you'll be like "ok, I'm having fun here solving cool problems, and you'll be like "this is work but this is cool" and sleeping at 2 am won't be a bother and believe me for a PhD program you must choose something you are interested in and even if there's no direct jon for it, research coz u like subject area and you won't just get a job you might possibly get a very good job at it and get paid well, but you must study what you like