re: Which is harder? Engineering, Med School, or Law School

As a physician I can only speak to medical school. As others have said it's less the complexity of the material (many early subjects you likely covered in undergrad, like anatomy and biochemistry, but it's much more in depth in med school) but rather the sheer volume. When I picked up my syllabus and content for my first exam I thought it was a hazing joke - literally a ream and a half of PowerPoint slides to study, for one exam. And that's for two years straight. Clinicals suck because there are still exams but in the meantime you're pulling scut duty on services.

Residency is an entirely different beast. Less didactically but instead you work 80 hours a week and still have to find study time.

But with all that said, I can't imagine sitting in an engineering class with all that math.