I should add, too, that these were the options presented to me to replace a dermatology rotation that fell through at the last minute. I wanted to do derm so I would feel comfortable whenever I saw some skin problem down the road, but unfortunately that's not going to work out.
I am sure that urgent care experience will likely be helpful, but I have been wondering what kinds of things I might learn from an allergy rotation, and if it would be helpful later on. And, who knows? If I liked allergy, I might even consider subspecializing in it. Plus, whenever I mention this story to classmates of mine, it seems like everyone responds by saying allergy sounds interesting. Choices, choices...