Family Med if you're talking about breadth covering kids, adults, elderly, and pregnant, the ability to counsel, and manage multiple medical problems on acute and chronic basis. Some is true for IM and Pedi I'm sure.
But if you're talking about high level complex pharmacokinetics & pharmacodynamics, I'd say HIV which traditionally has been a subspecialty, even within the ranks of ID physicians, but increasingly becoming more Primary Care (FM & Gen IM). Pedi HIV remains highly specialized.
Psych does a lot of off-label stuff that, as a pharmacist, you might be comfortable with, but the science is incredibly biased by drug companies.