Consider that USNWR itself has experienced its own uncertainties. The service academies and Harvey Mudd were at one time not in the National Liberal Arts category. Even currently, Coast Guard is not. Various other colleges, such as the University of Richmond, are also relatively new to the category.
The service academies are small. They have no/few graduate programs.
US News wants to stick them somewhere.
The “standardized” Carnegie classification for the USNA and USMA is “Other Specialized”,
not “Engineering and Technology” (like Harvey Mudd) … or “Baccalaureate/Liberal Arts I” (like Williams).
I don’t think they even grant BA degrees.
We now have two threads intertwining.
Regarding the original one… I add my vote for Reed being highly rigorous, and also support St. John’s College (Annapolis and Santa Fe) being in the same category. Many “Johnnies” choose to take a gap year between sophomore and junior year, in order to recharge themselves. The intense reading and thinking at St. John’s takes a toll on students.
Regarding the service academy thread… I oppose calling them liberal arts colleges because, well, they’re not. They do, in fact, belong to their own category – “military academy.” How can a liberal arts college NOT offer even a single Bachelors of Arts degree. Plus, a super-majority of cadets and midshipmen major in engineering; which is definitely not a liberal art. I think USNews only classified them as LACs because the academies don’t offer graduate degrees and the magazine wanted to rank them nationally. This simply shows the limits of such classifications.
I think USNews knew that it had kind of forced the issue when they categorized the U.S. Merchant Marine Academy as a “regional college.” USMMA only offers 5 majors, all of which are preprofessional. Even USNews could not put them in the liberal arts category despite being otherwise similar to all the other academies (and being far smaller, with only slightly over 1,000 midshipmen).
I like Marvin100’s list. If the service academies count, then of course they win hands down. I just don’t think that’s what the OP intended.
Harvey Mudd definitely counts. Why wouldn’t it.
I think Williams, Pomona and Amherst are a bit less than the ones above it, but I don’t think those could be ranked. Wellesley should also be in that last category.
It only offers 9 majors (none of them in the humanities or social sciences).
https://www.hmc.edu/academics/majors-at-harvey-mudd/
Although … given its course requirements, and the presence of the neighboring Claremont colleges, I imagine Mudd students are about as liberally educated as STEM majors at Williams, Amherst, Swarthmore, etc.
Harvey Mudd students could do an off-campus major through one of the other Claremont colleges.
Comparing Harvey Mudd and Amherst, Amherst has no general education requirements, while Harvey Mudd requires 11 S/E/M courses and 11 H/SS/A courses for its core and general education requirements. So there is much more assurance that Harvey Mudd graduates have gotten a well rounded liberal arts education than Amherst graduates.
Why would the degree title BA versus BS matter?
Ah, now we’re getting to the definition of a LAC. What is a liberal arts education? IMO it is one that incorporates requirements across a broad range of disciplines. Due to the core curriculum at the Academies I think they have one of the strongest arguments for providing a liberal arts education. Why does a school have to offer a BA to qualify as a LAC? The Academies give BS degrees to all grads based on the science and engineering classes everyone is required to take. You can still major in history or english. And we’ve all seen that some (relatively few) LACs offer engineering.
Some liberal arts colleges, such as Williams, Amherst, and Bowdoin, offer only the BA degree.
Others (such as Swarthmore) offer both the BA and BS degrees.
It is very unusual for a “liberal arts college” to offer only BS degrees.
According to the USNA site,
“Upon graduation, a bachelor of science degree is awarded regardless of major, by law, due to the technical content of the core curriculum” (italics added).
The USNA does allow students to major in English, history, economics, or political science … but not anthropology, classics, music, psychology, religion, philosophy, or sociology. Furthermore,
“For the Naval Academy Class of 2013 and beyond, at least 65% of those graduates commissioned into the U.S. Navy must complete academic majors in science, technology, engineering, or mathematics disciplines.”
That, too, is a very unusual feature for a LAC.
http://www.usna.edu/Viewbook/academic.php
To me, the essence of a LAC has to do with the educational mission of the school. The classic LAC mission is not career training. Nor is it leadership training for the nation’s defense, which seems to be the focus of the service academies (although many academy graduates, after completing their service obligations, turn out to be effective leaders in many fields.)
My general opinion on the topic is that a student can bring her/his rigour with her/him. If a student’s ethic is to master the course material available, while combining this with an interest in topics that have not been directly assigned, then many colleges could be rigorous and rewarding.
What is meant by rigorous?
If you mean leading the most disciplined lives from sunup to sundown, then the service academies are tops.
If you mean the most challenging academics in the sense of having to take many classes outside of your interests, then a school with a large common core.
If you mean most challenging academics in the sense that each class, whatever you take, is likely to be very demanding and you will be competing with other students who all are as talented and driven as you are, then WASP are likely to score the highest.
I think that if you mean “with the most intense workload”, HarveyMudd, Reed, and Swarthmore win. 
(Deep Springs is a good suggestion though but it stands in its own category).
“Harvey Mudd graduates have gotten a well rounded liberal arts education than Amherst graduates.”
But do they get that education at Harvey Mudd ?
Or is it essentially like a virus, where it needs to attach itself to a host school to suck out the humanities and social science courses that nearly every single other institution in the country that calls itself a “liberal arts college” actually has itself, on a native basis?
A number of liberal arts colleges share courses as part of consortia. But few others completely abandon huge chunks of the fundamental core bastions of what liberal arts colleges traditionally offer altogether.
Colleges that fundamentally depend on other colleges to fulfill their requirements and educate their students seem almost more like component schools of a multi-college university than typical independent, and self-contained, LACs.
^ Mudders are required to take a certain number of their HSA classes (I think it is 4 or 5 out of 11) at Mudd. It isn’t totally dependent on the other Claremont colleges.
It looks from https://www.hmc.edu/hsa/wp-content/uploads/sites/25/2015/04/HSA-Advising-Hdbk-2015.pdf that Harvey Mudd’s 11 course HSA requirement includes:
- At least 6 courses (HSA 10 and 5 others) taken at Harvey Mudd.
- At most 5 courses taken elsewhere, at most 2 of these from schools other than Claremont colleges.
Harvey Mudd’s HSA offerings may not be as numerous as many other colleges, but are numerous enough that a student can easily take all 11 required courses at Harvey Mudd if s/he chooses to.
All this naming of schools and…did I miss what major we’re talking about? That makes a difference. Imo.