I would love to recommend some core sites, but alas 🙄 I am only a MSI, so I can only go by hearsay...
Some of the sites are at major hospitals, like up in Michigan or Pennsylvania (Mercy), some are rural, and some move you around the city, like in Kansas City. It changes every year too, so they might add or take some sites away. For example, Botsford used to be a UHS cite, but we lost our DME person who handles the rotations there, so they dropped it. I hear it was a fantastic site too.
They have about 3 in Florida which I hear are poplular (but who knows, this could be strictly due to the weather). Most of the students either end up in the KC area (especially if you are in the UHS MBA program), and a lot of them go to the Ohio/Michigan area. I guess it all really depends on what you want. I hear Detroit Riverview is right in the heart of Detroit, and if you want to see gunshot wounds etc. then this is the place to go.
If you end up going to UHS, they have what they call, hospital day, where you have the chance to talk to all the reps from these sites and see what they have to offer.
There are a lot of sites, which is one reason I chose UHS, lots of flexibility to serve areas you are most interested in.