My D is a current premed at Brown.
Premed classes are very rigorous and will be wherever you go. For my D, the fact that everyone is collaborative rather than competitive was huge. The kids help each other and the profs would love nothing more than all the kids to ace their class. It’s about mastery of the materials, not who got what.
Brown students typically have higher GPAs, which is a huge help when applying to med schools. One reason for the higher GPA is, other than having to take classes recommended for med school, or needed for your major, you don’t HAVE to take any particular class. Another is that the first couple of weeks of every semester, you test-drive your classes and can add/drop/switch, no problem. That lets you get a good idea of whether the class will be interesting to you and if you like the way the prof teaches. You can also take classes pass/fail, but I think you need to use that sparingly because it won’t look very good to med schools.
I’d assume you can get similar EC experiences at both schools and similar abilities to work at hospitals etc. My D has some incredible experiences, and assume kids at Penn would have incredible experiences too.