Credits are deceiving I would say. There are always killer core classes, organic chem, and weed out physics classes that students may spend more than the credit hours to earn a B or A.
It may be more important to decide if a Quarter calendar will work for the student. Quarter calendars vary a little bit,
so Rose Hullman in Indiana, stretches quarter 2 over Christmas break, leaving the student with some work over Christmas some years. Most other quarter calendars start very late in September and end late, making it harder to sign up for east coast REU summer programs or government summer programs that start before the quarter calendar ends. Some students find Quarter calendars too intense and stressful, THINK: mid term/final/mid term/final/mid term/final.
Semesters are sort of more leisurely but if students load up, then not really. Some schools like Carlton College and Dartmouth U strictly limit the three course per quarter limit. Others may not, Stanford?? but you can get in trouble
quickly if you load up.
Also, look for late drop dates, which is FLEXIBLE. MIT offers one of the latest drop date that I know of, so student can actually fail the first exam and the second exam, and then bail out, and try again the next semester. If you drop too many though student may spend an extra semester to graduate, so its a double edged sword, a late drop date.
Another option that may play into decisions: Some colleges offer some pass fail grading for some classes, MIT, GaTech and Caltech offer some limited pass no credit options, so you can explore classes and not worry about getting a C or D. Swarthmore College offers a semester of pass/fail.