What's the cost difference?
I'll try to break it down a little. My s/o goes to Columbia so I'm pretty familiar with the school as well.
Specialties: Penn has the best ortho match numbers in the country, and Columbia has the best OS match numbers. However, you can match to each specialty at both schools. Columbia definitely makes studying for the CBSE easier, but there is a trade off - you don't have a GPA/class ranking so you HAVE to do well on the CBSE. Additionally, you are compared to your classmates, so (in general) you have to do on par with their CBSE scores. I'm a D2 at Penn and 7 of us have already broken 70 on the CBSE so it's definitely doable with our curriculum.
Living: With all due respect, Washington Heights is not a fun place to live. I'm not going to argue that West Philly is a great place either, but it's miles ahead of Washington heights. Miles. Many more restaurants, bars, grocery stores/regular stores, undergrad campus close by, SAFER etc. Center City is a 5 minute uber/septa away. Your perception of living in New York will change when you move to Washington Heights. It's not like what you see on TV. People start trying to move closer to midtown their third and fourth year, but rent becomes insane at that point. You want to go to Midtown with your friends on a friday night? A drink at a bar will be like $15.
Clinic/preclinic: As much as I don't like preclinic sometimes, ours is run really well. At Columbia, you have to share your instruments/supplies with classmates which can definitely be a hassle. Their faculty to student ratio is lacking and using D3s/D4s as TAs does not make up for a lack of faculty. At Penn we have 1 faculty per group of 7 people. They are devoted to just your group. At Columbia you have like 2-3 faculty for 84 people?? That's insane. Moreover, the first year at columbia you have preclinic 1 time a week for 4 hours. Since there are not enough chairs for everyone, you're standing behind your partner twiddling your thumbs while they drill and you watch. After 2 hours you switch with them. Talk about total waste of time.
Curriculum: Penn's curriculum is much more dentistry focused. No surprise here since we don't take classes with medical students. One large advantage with Columbia's curriculum is their P/F/take home exam grading system. With this whole pandemic thing, we're finally seeing what it's like to have take home exams and HOLY SMOKES its so chill. Penn will definitely be more challenging/stressful. I can't tell you how many all nighters I've pulled with my friends (lots of korean fried chicken has been eaten) studying while my girlfriend can go to sleep at 10 pm the night before her exam because all she has to do is pass. You're going to have to work harder at Penn no doubt; however, I
strongly believe you'll learn more about dentistry and come out a stronger dentist at Penn.
At the end of the day, it all depends what you're looking for and value in a school. Good luck.
Side note: you said the big class size was a downfall of Penn. I think its just the opposite. You're way more likely to find a solid friend group if there are 50 more people in your class. Also, you're way more likely to get sick of your classmates if its a small class. ALSO, even though Penn has a larger class, we get more individualized attention. When Columbia tells you the size of the dental class is 84, you forget that there are another 140 medical students in your class that you'll be spending the first 1.5 years with, so your class size is really like 220! NYU level
