hi drill and fill,
Although I haven't been to Columbia (I declined their interview) I really liked U Penn when I went to their interview. They have been known to get a lot of their students into specialty programs, especially oral surgery (the dean of the school is a very well-known oral surgeon). Their pre-clinical facilities are a bit out-dated, but they are building a whole new facility that should be done by next fall (I'm not sure what it will be used for... I think some kind of patient clinic). I like the fact that the dental school has their own faculty to teach the various didactic/science courses. I heard that at Columbia, you take your classes with the med students, taught by med school professors. Also, they have a couple of "dentsim" dummies that were the first in the U.S.... they are like computerized patients that help you practice your pre-clinical skills.
Those are just my opinions about U Penn... I haven't been to Columbia so I don't know a whole lot about their school. Hope this helps though!