And none of them have ever taken a class at Harvard.
It is my sincere hope that both schools deliver rigorously stimulating opportunities to all of their students, but arguing which is more difficult or correlating grades between two schools is pointless.
The best way to get any sense of rigor is through transfer students. It’s not perfect, but students who move between schools are a good measure of relative difficulty. The two recent examples I know personally have gone from Ivies (Cornell and Penn) to LAC’s (Swarthmore and Amherst), and both believe that the rigor and breadth of material covered are greater in the LAC’s.
The OP wants to know where it’s hard and where it might be a bit easier. As a general rule, I’d suggest anyone looking for a better work/life balance attend an Ivy.