Cheerio
It sounds like the interviews conducted on-campus are more laid back. I wonder if this means it's better to make the extra effort to go on campus and do the interview there.
Don't get lulled into thinking that. The Ross blog last Fall mentioned something about applicants not taking the interviews with current students seriously enough. I'm not saying that to make you nervous, just to make you understand the importance of treating it professionally.
Personally, I'd like to be interviewed on campus. You have a set time limit (30 minutes), will get AdCom approved questions, get to talk with someone actually in the current program, and get to show your interest in the program. That said, I actually enjoyed all of my interviews. I was well prepared and made sure to remember that about half of the interviewees will be admitted vice one of X for a typical job.