“Class sizes are not likely to be similar at Michigan and Penn, actually. At Mich, 48.1% of classes have fewer than 20 students. At Penn nearly 70% of classes have 20 or fewer students. Meanwhile at Mich, 17.6% of classes have over 100 students compared to only 10.6% at Penn.”
PennCAS2014, the 17.6% and 10.6% of classes at Michigan and Penn have over 50, not 100 students.
At any rate, while it may seem that Penn classes are much smaller than Michigan classes if you look at classes with fewer than 20 students, things even out nicely if you were to include classes with 20-29 students. Overall, 79% of the classes at Michigan have fewer than 30 students, compared to 83% at Penn. I never denied that classes at Penn are smaller. All I said is that the difference is not significant.
"Additionally, while the programs mentioned are indeed popular, Penn often offers both large and small sections of intro classes to ensure that students who want to take intro courses in a more intimate setting are offered that opportunity. "
That’s the same at Michigan. Larger lectures will typically be broken down into smaller discussion sections. Those sections usually have anywhere between 20-25 students.
“Additionally, the student to faculty ratio at Michigan is 15 to 1 compared to Penn’s student to faculty ratio of 6 to 1.”
I see Penn fooled you with their misleading data. Michigan is honest enough to include graduate students who are enrolled in colleges that also enroll undergraduate students…is Penn? 
Seriously, in order for Penn to come up with its 6:1 ratio, it had to include 9,500 students in its calculation. That’s very suspicious considering that Penn has 10,000+ undergraduate students and another 8,000 graduate students enrolled at Wharton, the SEAS, Nursing and other programs/colleges that enroll undergraduate students. If Penn calculated its student to faculty ratio like Michigan does, by including graduate students, its student to faculty ratio would be 12:1, not 6:1. And omitting graduate students from the ratio is very misleading, since graduate students drain faculty resources as much as undergraduate students.
“To me those were large differences when I chose Penn over Mich (for the college, not for engineering).”
Only there differences aren’t large at all…not because Penn isn’t exceptional, but because Michigan is also exceptional. Unfortunately, statistics can be manipulated to make it seem like there is a large difference between Michigan and Penn, but the differences are in fact insignificant.
“And, while it’s probably(?) true that if you lop off the bottom quartile at Michigan you would have a student body with numerically similar standardized test scores to the average students at Penn, you would also be cutting out nearly as many Michigan students as there are freshman at Penn… It’s a lot of people to pretend like they don’t exist.”
Who is pretending they do not exist? To you, those students may be unworthy and may be an embarrassment, but they are very much an active part of the Michigan community. They enrich the academic and social environment. Many of them are gifted in other ways, be it artistically, musically, athletically etc… The point I was making is that overall, the Michigan student body is intellectually switched-on and the learning environment at the University is vibrant and rewarding.
“Overall, both institutions have good brands with high research activity-- the undergrad experience at each, however, will differ markedly.”
I disagree completely. Michigan and Penn actually offer similar undergraduate experiences. They are obviously different in many respects, but not in ways that makes one better than the other. It goes without saying that Penn is exceptional, but there is no need to try and make it out to be superior to one of its peers. If you were to fairly analyze Michigan, I am not so sure you would dismiss it so easily.