I received a PhD offer from Columbia (but not IEOR) and went to Columbia for a campus visit last week. My potential advisor has a strong connection with the professors from IEOR department, and I had the chance to meet with one professor from IEOR. Though I am not familiar with the department, I feel there are many possibilities here. Do you know there is a Data Science Institute here? They are uniting professors from different backgrounds to utilize the "big data" and bring more insight. Many professors in IEOR has contributed a lot to the institute. It's really a promising place for me.
Also Columbia's location is great. Chances are you might live just a block away from your advisor, because many people live in the school housing due to the notorious housing price in Manhattan...Maybe it's bad... but I just want to say it's like a small community of faculty and students here and the security within the campus neighborhoods is great I think. Generally you don't have to worry about the rent as a PhD student.
I am not familiar with Berkeley IEOR. But I had a feeling that if I received its offer (in my major) I would definitely choose Berkeley... It's always my dream school. California dreaming! Anyway I hope you'll get some different perspectives of Columbia here. I think I will accept Columbia's offer in the end.
Best wishes!
