@4101297 Penn is the stronger option here overall for undergrad, and especially for your major. If there is nothing you absolutely love about UMich above all else or something that you really hate about Penn, I would go with Penn (and most students in your position do so). That said Umich has an awesome polisci department.
Btw here are some cool resources/initiatives at Penn might interest you given your major.
https://piw.sas.upenn.edu
https://pennbidencenter.global.upenn.edu