Owgmkll:
While an interesting question, I don't think this is one that can be answered with tons of certainty much less quantitative evidence. It's not quite like undergraduate where there are much more rigorous programs than others. Business school is an academic experience but as many will tell you, it's also very social and professional. Some people go to b-school to pivot careers. Others go simply to network and travel. Many go purely for academic purposes. Most go for some combination of the above. The point is, it all depends on your priorities and how you choose to spend your time as an MBA student.
Grades simply don't "count" the same way they do as undergraduate programs, law schools, other graduate schools, etc. So many b-schools have non-grade disclosure or grading systems that aren't even on a 4.0 school. When you take that all into account, it makes providing an answer even harder!
Others will hopefully opine here, but you should talk to students who share interests with you to get an understanding of the relative difficulty of the program. Yes, some programs are more demanding or "serious" about class time. HBS, for example, has classes 5 days a week but that doesn't necessarily mean they are that much harder since the "1-2-3" grading scale (all technically passing marks) makes it really hard for someone not to graduate.
The point being, I would focus on getting into a solid program that's an appropriate fit for your interests and goals. That will make the experience "easier" because it's one you enjoy and makes sense for you.