Hi caulfiedh. Congratulations on your admissions! They are both great and you can't go wrong! Do you mind sharing your profile with us?
Regarding your question, I though ORC is more varied than ORFE. Like the name suggests, ORFE (Operation Researchs & Financial Engineering) puts a lot of emphasis on finance applications of OR. The ORC on the other hand is quite broad (http://www.mit.edu/~orc/research/activities.html). I'm sure there's room for your interest at both though. Remember to consider the location too, since both choices are very good already. Princeton is a very pretty campus, and if you like quietness so that you can concentrate on working very hard, Princeton is great. MIT is in the middle of Cambridge/Boston, it has lots of student activities (for grad students too) and the city itself is good to live for a student.