Hi,
I had Wharton interview during round one and am currently in the waitlist.
For choosing an interviewer,
1. I googled every candidate and tried to find out more about them.
2. I took advantage of my networking.
All of my interviewers (Wharton, Columbia and Chicago alum) are working in the financial industry as I am, and therefore it's no surprise that we'd have friends in common.
For pre-interview preparation:
1. I highly suggest that you email your resume to the interviewer after you make the appointment with him/her. (Do not think that the school will give any of your info to the interviewer though you need to upload your resume when confirming the interview.)
2. Be sure to remind your interviewer (in my case, by email) about the interview one day before the interview.
3. Be sure to take two copies of your resume with you to the interview. (Great, now I'm like a nagging mom.)
4. Needless to say, prepare for the interview questions and do mocking(s).
Try to make your answers concise and precise.
Try to start each answer with a short conclusion and then elaborate accordingly.
My Wharton Interview:
1. I did the Wharton interview with Vincent Wei-Chung Wang (Class of 2007) in Taipei. He is working for IBD of CDIB (中華開發).
2. Vincent is a nice and responsive interviewer with a friendly smile on his face.
It took about 40 min for the official English interview, during which Vincent conversed with me back and forth.
We began with my self-introduction and then he asked questions about me accordingly.
His style is more conversational than "Q&A".
With that said, I believe that interviewing with Vincent, you can really "be yourself" without efforts on preparing for "surprising questions".
After the official interview, we chatted in Mandarin for another 2-3 hours.
Vincent was quite helpful in answering my questions regarding MBA and Wharton.
Other Information:
Another interviewer you might find in your list is Jonathan JJ Lin. Jonathan is working for IBD of Deutsche Bank,Taipei. I met him once in an event. He is also a nice guy, but he was not shown in my list.
Both Vincent and Jonathan are NTU alumni.
Good luck.

Applying for full-time top MBA programs, 2008 Fall entry.