<p>"I think Calc 3 is harder, because you have to look at integrals and figure out which method to use, or look at sums and figure out which test will tell you if the sum converges. DiffEq is more straightforward. It’s usually pretty easy to tell what differential equations can be solved with what techniques, and many of the techniques are pretty fun.</p>
<p>But also note that I took DiffEq at a community college and did Calc 3 on the AP test, so that might skew my opinion somewhat. "</p>
<p>Umm do you mean you took calc 3 after you took the AP test for calc BC because the standard topics in multivariable calculus aren’t covered in BC (otherwise known as single variable calculus)</p>
<p>The type of integrals I had to set up and solve in Calc 3 were much harder than the stuff I did in elementary ordinary differential equations.</p>
<p>"Diff Eq is one the toughest (perhaps THE toughest) required math course in engineering curriculums. "</p>
<p>What do you mean by the toughest required? I know engineers use PDEs and I know electrical engineers might do a course in Complex Analysis</p>