I've had 3 rotations so far (IM, Surgery, Ob/Gyn) and I can't say that I honestly despised any of them...I had something to learn from each rotation, as each offered its own sets of challenges (whether it be concept-wise or interaction-wise)..
nonetheless, of the three, i disliked IM the most. although both surgery and ob/gyn were beasts (and this is ESPECIALLY true of ob/gyn, which I just finished today), I just found IM to be monotonous and predictably boring, with the same chronic diseases being presented to me, over, and over again..
I've yet to get through a few of the other rotations. Maybe I'll change my mind by June. Who knows?!