Which would be more beneficial when applying to theoretical physics PhD programs, Math M.S or experimental physics M.S.? I am graduating this semester with a bachelors in physics. My goal is to do theory in my graduate level course work. The problem I am in now is that I missed the deadline to take the physics GRE (I'm taking it in April) so I also missed the deadline to apply to most graduate schools. Fortunately, I was accepted to pursue masters degrees by both the math and physics departments of my current school. My plan is to do one or the other and apply to other schools next semester. My question is which one will be more beneficial to me? Our math department is all around phenomenal... but it won't say "physics" on my applications. Our physics department is good, but it is completely geared towards experimental nuclear physics, which is not my interest (and there is no non-thesis option). Every day now I have been swinging back and forth; math... physics...etc. So, which one would be more beneficial when applying to schools with top theory programs, Math M.S or physics M.S.?
If your MS in physics will be experimental and you want to do theoretical physics, the math route could work. But we are basically guessing at how an admissions committee will see your application;  so I encourage you to keep asking. Hopefully other answers here will help.