Hi moving_up. I'm actually currently making the same choice but for their PhD programs in biostat. I've also seen Minnesota ranked higher, but on US News the difference is pretty minimal (i.e., for biostat departments they are 6th and 7th respectively, separated by 0.1 on the survey score). Based on that I don't think it would be "foolish" by any stretch to turn down Minnesota for Penn, but I'd be interested to hear if you've seen more significant rankings differences than the US News rank.
I'm also not sure how much of a role this plays for the masters program, but Minnesota has some specific strengths over Penn (while Penn is arguably slightly more well-rounded). Specifically, from what I've heard Minnesota is very strong in clinical trials and bayesian methods (especially those used in clinical trials). There you would likely get a chance to take a course taught by Brad Carlin, who is very well-known in those fields.
I'd love to hear more thoughts from you and other people though. I'm leaning slightly towards Penn at this point, but I still don't have as much information as I'd like.