You should look up the med school entry stats for each school. If I’m remembering correctly, brown has a higher med school matriculation rate than Uchicago. I’m not even sure if that matters at all, but maybe someone else can speak to that.
My son got into both and opted for brown (and he’s now a phd student at UCSF with a NSF grant, and he thinks the latter was possible bc brown had terrific opportunities for lab research and for volunteering as a science educator in the providence high school system, two things highly valued by grad school committees and the NSF readers). Both schools appealed to him because both attract an intellectual student body and while he was a STEM kid, he loved the humanities too, so many of the Core classes were right up his alley, and he duplicated that coursework at Brown. Also, uchicago at the time (for the 2015 class) didn’t offer a neuroscience concentration and Brown has one of the leading undergrad neuro programs, which certainly influenced his decision. (I think Chicago may now offer that major, and Yale just announced that it, too, will offer the major, but clearly, brown has the advantage of having a well-established program.)
Certain courses at Brown are going to be back-breakers, like the 2 orgo courses, and my son took some graduate level applied math and neuro courses, and also took what’s considered the harder physics sequence, so it was plenty rigorous but brown is on the whole a collaborative environment. He was certainly stressed at times but really, truly loved his Brown experience.
His high school GF went to Uchicago as a bio major, placed into the honors sequence there because of her AP bio 5 score and her 800 in bio, and had such a hard time barely getting a B that she dropped out of the major by the end of her freshman year. It was clear to her that her GPA probably wouldn’t be enough for med school or a top rated phd program. I felt badly about that bc I knew she was highly intelligent and a kind, thoughtful person who would have made a wonderful doctor. Perhaps had she gone someplace else, she would have been able to stay on track but her confidence took a beating and she just didn’t want to struggle like that through the rest of college. She switched her major to poli sci.
Also, finally, I’d suggest you look up Brown’s med school advising page. I’m not sure that you’d be advised to take any of your med school courses pass/fail, or how many non-STEM courses even. I think the only courses my son took pass/fail were those that were mandatory pass/fail, like one of his grad level courses and his English writing courses.