The best way to answer your question is to contact the admissions office directly. However, it seems that UPenn really prefers some work experience (the avg for last year's class was 4.5 years) while Pittsburgh will consider applicants with strong academic records even if they lack work experience. The bottom line is that you need to convince the admissions committee that you have enough experience to contribute to classroom discussions and also understand how the concepts you're learning apply to real-world situations.