Really, do whatever you want. The only time this came up in interviews was:
A) What has been your exposure to radiology? - So make sure you've done at least your place's core radiology rotation, I'd also recommend at least one away or a subspecialty rotation (IR, Neuro, Peds, whatever). Show's you're actually interested in the material.
B) What rotation are you on now? This is just making conversation, I think. Anywho, I was actually on interesting rotations during my interview season so it was cool to talk about them and how the attendings/residents were teaching me radiology from their subspecialty areas point of view. But if you're in a blow-off rotation because you need time off to interview, or on vacation, I don't think there's any "Meat" to this question.
C) What non-radiology rotation did you enjoy the most? Enjoy the least? For me, this was an easy question because it was in the field that I was considering versus radiology. It just shows you have passion for medicine in general. As for least: I said OB/GYN and the interviewer said "Yeah, everyone says that one.' so I think it's a safe bet 🙂