I don't think it makes any difference on the interview itself. I think it would be a little better to interview at home, with someone from the same culture as you, since you can build a connection with ease. You also build a more personal connection, since the admissions office will probably be interviewing dozens of candidates each year.
Also, I've seen that alumni want to have the biggest number of people from their home country going to the school they went, so they might over-promote you if you do well on the interview. That's just a thought and I have nothing to back that up.
On the other hand, visiting the campus can give you a very good idea of how the school works, specialy if you spend a day or two at the school before the interview.