EssaySnark says, Stern's P/T program is somewhat less competitive, though by no means easy to get into. GMAT and GPA ranges are considerably looser for Langone P/T. And, sometimes Stern still has slots available in the P/T entering class just a few weeks before that class begins (e.g., right now, they're still accepting apps for the September start). The curriculum of both programs at Stern is identical and the faculty are the same. EssaySnark has heard that the P/T program attracts slightly older students. Some schools' P/T programs are very segregated from the F/T program with little opportunity to network. It's often tough for P/Ters to participate in the same clubs and student activities, just due to scheduling constraints.
Probably the most important difference to note is, Stern does not allow Langone P/T students to participate in on-campus recruiting for internships or first jobs, because the P/T people already have a job. So, the P/T program would not be appropriate for career-changers.
It's important to express in the Stern P/T app not only why MBA and why Stern, but also why Langone (all three).
Last point, and this cannot be overstated: Quality of life doing a P/T MBA and F/T job SUCKS. Especially if you have a family. And you're doing it for like three years or something. It is GRUELING. F/T program is much much much better for this reason alone. Being able to focus only on school -- and getting through it faster -- makes for a positive experience overall.
