Monique-I have been accepted to PENN and I plan to go there this fall. Although I am not a student I have done quite a bit of research on the program. Some observations:
Penn is a much larger program, more profs, more students, more classes. Perhaps less attention for the individual student as a consequence? I don't know. Current students at PENN have told me that the profs are accesible, however.
New York City is generally thought of as being a nicer city than Philly. However the PENN campus is very nice and green yet 5 minutes from downtown. Columbia is relatively far from downtown and midtown and the campus is not as beautiful I hear.
I heard that urban planning at PENN in the early 90's had some kind of crisis. But it seems that they are fine now. They have traditionally been the GREAT planning school, more planners come from UPENN than from any other school in the US.
To be honest however there isn't a pecking order like law schools or business schools. There is a group of stronger schools-- UPENN, Columbia, Berkeley, MIT, UCLA, Georgia Tech and a few others.
PENN has some really nice facilities, the arts library is amazing. I'm not really acquainted with Columbia's, though.
PENN also has a very good, PHD program one of the three or four best so it might be possible to stay on after the master's if you really like planning theory. The same is more or less true for Columbia, though.
I've contacted some PENN students and they seem happy with their program and it sounds like the atmosphere is really nice there.
Finally, planners don't make as much money as say MBA students so debt is harder to pay back. If one school offers much more financial aid, you should definetly take that into consideration. I hope I've helped you some. Hope to see you at PENN, this fall. If not, enjoy New York!