Woops, I just voted for Ob Gyn - I though I was in the "specialties I like the least" thread.
The more responsibility I was given and the more teaching that the faculty and residents did, teh more I liked the rotation - regardless of the specialty.
Psych was awesome - I got a lot of dental work done the month, designed a custom engagent ring, and proposed to my fiance on a backcountry ski trip in Colorado. I got a grade of Satisfactory - I think because I was only there half the time. When I was there, 3 weeks were boring shadowing in an interesting area (adolescent). The awesome part was the other 3 weeks in general psych: I got to see all my own patients and then go discuss the management with the attending. Out by 3 on the latest day.
Family - I really enjoy working with FP people. Usually they really care about their patients. One if my attendings did house calls for home hospice patients and she took me along - a powerful experience. I also got to work in an urgent care clinic for 2 weeks during that rotation. That was awesome because it was more acute stuff in younger patients with thinner charts.
Medicine and Surgery - both painful for their own reasons, but when I look back, I learned so freaking much on those rotations. They were both awesome for that reason alone.