The Daily Pennsylvanian reveals that Penn, along with 22 other new schools, will accept the Common Application next year, but will also require a Penn specific supplement. Penn is joining the roughly 300 schools that already accept the Common Application.
Penn Admissions Dean Lee Stetson said that Penn is allowing the Common App to encourage application from minority applicants. At the same time, the supplement will enable Penn to continue obtaining the distinctive information it has requested in the past.
The degree of difference between the common app with supplement and the unique Penn application, which Penn will continue to offer, should determine which option you use. If the difference is significant, then use the unique Penn application, if at all possible, because it will reflect what Penn really wants to know. If the difference is minimal or non-existant, then use the Common App plus supplement, because it will be easier — provided you are applying to other schools that also require the Common Application.