That idea is a nice luxury, to interview auditors and then select, but it is not always practical. Perhaps if the auditor is local, or a new auditor with an empty schedule, they could stop by for a visit. But, for experienced auditors, our schedules are generally very packed months in advance. It is uncommon that I have the availability to visit a prospect that would like to meet me first, unless perhaps, I am local, or will be in that area. If you insist on that, you run the risk of getting a rookie assigned. Then further, even if you like the auditor, after a few years they are likely to cycle out and a new one is assigned.
As far as recommending registrars, I am a CB auditor, so I realize my recommendation is not completely unbiased. However, I am also a consultant, and have to frequently make recommendations to my clients.
As an independent, I can chose which CB's to affiliate with. I have chosen to affiliate with Smithers Quality Assessments, and am beginning to develop a working relationship with NQA-USA. I selected both of these organizations because I feel they both do good work for their clients, try to be customer focused, and try to provide value-added services, and have integrity. I have chosen to affiliate with them for that reason.
I would also suggest to be very careful if you are considering Eagle. I used to recommend them, and have clients registered with them. But they appear to have changed and become much more difficult to deal with, especially in TS.
Good luck in your search...