Truth be told, neither class will be of much use to you in med school or beyond. Take the course that you'd enjoy more.
P-Chem, if you like math, theory, and rote problem solving. P-Chem shows you how many half truths you were told in gen chem. Pretty much everything in gen chem is a half truth or a limiting case of something more general. I liked this class because I like to know how and why things are the way they are. But P-Chem is tough!
Quant, if you like precision and/or creativity in problem solving. By the time you get done with this class, you will be irritated whenever you see statistics used incorrectly or in a devious way (i.e. by marketing people). I liked this class because the chemistry problems were challenging in a thinking way, not in a grueling math way (the latter is more P-Chem).