Hmm, tough question. I've never pictured him with either. Actually, I've always pictured Rolf as being so * around by fate and the loss of his family (including Nei) that he's not really interested in finding love. If it's after the whole mission, then I'd say maybe Amy*, but that's mostly because I picture Shir not being able to settle down. After all, she's Shir of the Wind!
*In my own mind, though, I think Amy has a thing for Rudo, or they have feelings for each other, maybe. I think the patient/doctor, protector/protectee(?) relationships they have with each other bonds them over time.
Have I thought way too much about this? Yes I have!