I got into both of these schools last year, Penn with 21st century scholarship and UCSF off the waitlist. A couple of thoughts on these schools. Both are amazing schools, very prestigious. My gut feeling is that UCSF has a little more oomph behind its name, but in the grand scheme of things this is such a small difference that on an individual level it won't make any tangible difference for a medical student. Also Penn is a big name on East Coast, UCSF on the West Coast. Which do you prefer? If you wanted to spend your entire life on the East Coast, I don't think it would make much sense to go to UCSF.
The P/F 3rd year is a huge plus for UCSF. I felt like Penn has a reputation of being a little more intense. However, at this caliber of school, there are ambitious people everywhere and realistically a student may feel overwhelmed by their peers even if one place is more "chill." Anecdotally, I felt like UCSF had a less competitive feeling, but it also felt less cohesive as a class, people lived throughout SF, two campuses 30ish minutes away from one another, and state school = more bureaucracy and administrative hassle for sure. Also a point my host made at UCSF was that yeah it's chill but its still a top school, people want to succeed, and for some that may create a more intense environment.
Facilities much better at Penn, but I personally feel that once you get into the grind of things how much does it matter? I'm also not exactly sure about the nuances of the curricular differences between the two schools, but from what I remember from last year they were a pretty similar set up, systems based with a lot of small group stuff. But I could be wrong. After talking to a lot of people, I'm not sure how much those things really matter.
For me personally, if money truly was not an issue, I would've chosen UCSF. I enjoyed the interview day here and the overall vibe, and I personally could see myself ending up on the West Coast. Otherwise, both are great schools and I think personal factors and where you see yourself will play a big factor in your decision. Feel free to PM me if you want.