Oxford v. Cambridge for the Liberal Arts?

My major will definitely be STEM. Also, I am perfectly aware that the UK higher education system does not really advocate mixing subjects together - instead it seems you are given a pretty focused path the moment you pick your major. However, under the false assumption that these are my only two choices, I am asking this question (I will definitely be applying to US universities).

I love the environment at Oxbridge (I think much more so Cambridge) but would also like exposure to the arts and humanities. My hypothesis was that, since Oxford is more focused with the humanities (shown by the existence of the “Physics and Philosophy” and “Computer Science and Philosophy” courses), being near the students there would be helpful to my goal of combining some amount of arts with my scientific education. Also, I could take one of those two courses to be exposed to one aspect of the arts (philosophy). Is this completely untrue, and I should just apply to Cambridge since I like the college town feel of it? Or is it valid to apply to Oxford instead so I can take advantage of the (albeit few) options they have to engage in both the arts and sciences, both directly through those two courses and indirectly through the people around me? (this latter part might be perfectly accessible at Cambridge by living with people that study the arts).

I don’t think you understand how the system works. Unless you are admitted to a given course you won’t get supervisions/tutorials in that course. Sure you can go to the lectures, but those are large and non-interactive. Lecturers don’t set work, the supervisor/tutor does. So you could listen, but would you learn much more than by reading a book?

And none of this addresses the issue of getting admitted in the first place. You have to convince the interviewer that you love your subject more than anything else in the world, and want to (and already do) spend all your time on that.

What @Twoin18 said. Go spend some time reading the course descriptions on each website. They are extremely detailed, right down to what you study each year.

Would the Human Sciences degree at Oxford be of interest?

If you want a prestigious UK university with some choice in classes during your first two years, look into UEdinburgh, UGlasgow, St Andrews, and Aberdeen (the “4 Ancient ones”).
You could also look at the Quantitative oxial science at LSE. It’ll be very quantitative but you’ll be able to take other classes.