I know that medical physics pays really well if that is what your asking. You could probably find a job in medical physics just about anywhere because radiation therapies are becoming a standard in most hospitals.
I don't you shouldn't pick a speciality just because it will give a high paying job with good placement.
You can make lots of money with just about any physics PhD, and at the same time you can make not so much money with just about any physics PhD. Same goes for a bachelors degree. When you pick a specialization, you do it because that's what you like and what you want to work with. The job you get after might just come about from luck of the draw.