i would also like to add that it's not just the subfield that matters most, but your research approach/method--the more quantitative, the more desirable. i don't totally agree with this, but my partner is currently a professor in the social sciences and this is definitely the case.
i also want to echo fidelio's sentiments as well that an economic perspective has taken over the way we view education. psychology has had it's ups and downs, sociology was once a respected way to understand education, and now econ. who knows what will be next...
in short, focus on what genuinely interests you and what you are good at, and do it well. the rest will follow
