Congrats on some awesome options! I'm from AZ, so just wanted to share a bit about my perspective in case its at all helpful. The medical school is pretty inconveniently located, imho. It's really on the outskirts of even Scottsdale, which is already on the outskirts of Phoenix. Scottsdale is fine, but quite ritzy/snobby. Pretty good night life in "Old Town." Phoenix is miserable in the summer, but beautiful in the winter--especially if you're into hiking and outdoor activities. You are close to southern Cali though, which is nice! Also, regarding the match list at Mayo: this is hearsay, but my friend said that Mayo Phoenix has been a bit disappointed with their match lists, so I don't necessarily think it's just people matching at their first choices in seemingly non-first-choice places (I hope that makes sense lol). Also, I'm not sure if you're interested in working with underserved populations, but I really don't see Mayo giving you that much exposure to working with low-income/disadvantaged populations. I didn't really loveee working with the medical students there, but if you got good vibes, that's awesome!!
As for a positive, I've heard that at least in past years, the school tries to match personalities in the class to make it a good environment. Not sure if they still do this, but I'm guessing it's their attempt to make sure that the 50 students are relatively balanced in their personality traits. In practice, not sure how this works out.
If it were me, I'd pick Northwestern, but take that from someone who has somewhat negative opinions of Mayo Phoenix (as I've detailed above). Since money is still important, I would say that Pitt would be out for me because it's significantly pricier than your other options.
You've got this <3 Sending you my best, and let me know if you have any follow-up q's or if you just need someone to bounce ideas off of. No matter where you end up, you'll do great!