I was not TOTALLY sure about the future, but was leaning toward surgery or peds at the start of the year. This is how I lined up:
OB/GYN
Medicine
Surgery
Xmas break
Peds
FP
Psych
At my school, this is "front-loading", or putting the most time/labor intensive rotations first, and it was a grind, but it feels great now on xmas break. OB/GYN was its own field, so you don't need any previous clinical experience, and there was some minor surgery and lots of good times at births. Medicine helped me immensely for surgery, and I had more time on surgery to study surgical decision making, indications for operations, operative technique, tons of time to review anatomy/approaches, rather than learning how to medically manage surgical patients. In other words, I had more time to practicing thinking like surgeons think because I already had a firm hold on medical principles from the previous rotation.
Can't give advice on how my last three choices panned out, as I have not had them yet, but they are more of the fun/happy/crazy people times, so I am sure they will be easier going than the first three.
To sum up, I agree with above posters that "MEDICINE 1st, but not the absolute 1st" is the way to go.