Princeton used to have a hospital within walking distance of campus (University Medical Center of Princeton), but recently the hospital packed up and moved about 4 miles away on the other side of Rt 1. This makes it VERY difficult to do any volunteering at the hospital as an undergrad, especially since you won’t have a car.
The research opportunities at Princeton are wonderful, but most heavily geared towards molecular biology and very little clinical work being done on campus.
Duke on the other hand has a world class medical school on the same campus as the undergrads. As an undergrad you can easily interact with med school faculty and work in their labs.
Also take a look at the Princeton grade deflation. I’ve heard they’ve relaxed things recently, but in the past it was very difficult to get a top GPA as a princeton undergrad due to steep curving policy.