Hi!
I just matched in OB/GYN last week, and now feel better qualified to give advice on this topic.
Overall, my interviews went way better than I was expecting. By the time you're in the door enough to be offered an interview, it seems to really be all about personality and fit. I wasn't asked medical knowledge questions during any interviews (in fact, I got the impression that many programs were specifically avoiding those types of questions for the most part...) and was only asked to perform technical skills (knot tying, laparoscopic box while talking to a fellow, origami) at one institution.
I have always been in California thus far in my life, and found that the most "confrontational" (but mildly so) questions happened while I was interviewing at places farther away, mostly regarding whether I was serious about a program enough to move across the country or why I would ever leave California. I highlighted (or plastered?) my dedication/interest in Family Planning all over my application to screen out programs whose values did not align with mine, and found that in certain geographical areas where abortion care is more restricted, I was specifically asked why I would want to leave a liberal state like California to come there and perhaps have a harder time becoming trained in FP during residency.
As far as my rank list was concerned, it was all about feel and feedback from trusted people who had experience at the program I was considering (and a little bit about preferred location). I went into the whole process searching for a place who really took care of their residents and had a very supportive and nurturing culture, so that was my absolute #1 priority while ranking. To figure that out, I would ask questions like "What is your wellness curriculum?", "If one of your residents had a life event and needed to take time off, how does that work at your program and what support is available for that person?", "Has anyone ever left your program early? What were the circumstances surrounding that situation?", and (specifically to residents) "What advice would your significant other give my significant other if I were a resident here?". It was helpful when I knew faculty who completed residency at a certain program, prior graduates from my school who are current residents there, or classmates who rotated through a program who could tell me their stories about their experiences at certain places, because it gave me a better idea of how programs treated different types of learners.
Aside from culture, I considered whether the residents left feeling like good surgeons and well-rounded generalists right out of the gate, which is surprisingly not a given upon graduation from residency; I had a few residents at a top-tier program tell me that they do NOT get enough hands-on surgical experience due to there being so many fellows. Great surgical skills after residency is something that I want whether I decide to pursue a fellowship or not, and I wanted a program that supported what I wanted to do with my life. I didn't want a place that would try to push me into fellowship, but I also didn't want to go to a place that would preclude that possibility/make it difficult for me to be competitive for fellowship.
In the end, I loved a program near me and I loved a program that was far away. The far away program is very well-known, but logistically, the prospect of moving across the country and missing out on some important upcoming life events happening with people who are very close to me won out. I matched to my #1, which is a place that I believe can give me everything I want, and will also allow me to be in my friend's wedding in August and attend the birth of my (theoretical) future god children that my BFF from grade school is planning on trying to have in the next few years.
I hope this helps! Good luck!