I made this same decision when I was heading to college (for what it's worth, I ended up choosing Pton, but I'm sure I would have been happy at either place).
To address a few points:
Some things I've heard
Pros for MIT: More accessible to hospitals, better research opportunities, easier classes (if you're not an engineering major).
I can't imagine that MIT has significantly less difficult classes than Princeton, but I suppose you can seek out classes with an easier reputation at either place. It's probably true that more hospitals are accessible in Boston - Princeton had one hospital within walking distance, but I think they're moving the Pton hospital to the next town over soon, but lots of students use summers/breaks for shadowing, etc. And you can borrow cars from the school for off-campus volunteering, which lots of people do.
Pton has great research opportunities for undergrads because it's an undergrad-friendly place, everyone has to do a thesis, there is often summer funding available, etc. One thing I've realized is that because Pton doesn't have a med school, you'll generally be doing more basic vs. translational/clinical research while you're there - so if you reeeally want to do clinical research, you might have to do that off-campus, over summers and whatnot. But overall, definitely good research experience readily available (and required! for thesis).
Cons for MIT: Not as much pre-med guidance as compared to Princeton. Lower medical school acceptance rate (around 75-80%)
Pros for Pton: Med school acceptance rate is >95%. More guidance, "better" name i guess?
Pton's pre-med advising is quite good, in my experience. Accessible, honest, and generally helpful. It is true that they may discourage you from applying this cycle if you are truly not competitive, which may contribute to the high med school acceptance rate, but that's really just honest evaluation, which I appreciate. Nevertheless, I don't know that they'll actually straight-up turn you down if you desperately want to apply right now - besides, they've got a good idea (and years of data) about what kind of Pton student is successful in applying, and you've got good leeway. And they'll support you in exploring different ways to improve your candidacy if necessary.
When you are applying, they help keep you on the timeline, make suggestions about school choices, and are very timely with committee letters (unlike some other offices mentioned on SDN).
Cons for Pton: Grade deflation is a big one. I've heard mixed things about this. Some people say that even MIT has Grade deflation.
Don't worry about this too much. Yes, the grade deflation policy exists, yes, people complain/debate/etc a lot. Its effect on you depends a lot on what classes you're taking, what professors you run into, etc. I can talk about the nuances, but I'm rambling on enough, so PM me if you want elaboration. Besides, from what I've heard, de-facto "grade deflation" exists at MIT because (1) people are taking largely engineering/natural science classes and (2) so many classes are friggin hard.
The other main thing is that for me, MIT will cost about 50k, whereas Princeton will cost about 25k a year.
25k a year is a LOT of money, especially when you're considering going to med school - I'd advise you to go to Princeton. I liked lots of stuff about MIT (the culture, creativity, Boston, etc), even though I ultimately decided not to attend, but the money reeeeally tips the scale towards Pton.