There are different schools of thought regarding this.
Here are my personal opinions...you got two options...start easy or start hard.
BUT...I would not recommend starting on medicine. You will start the rotation with a bunch of students who are at the top of their game because they're fresh out of 2nd year med school, just took Step 1, and will know a lot more than you could ever remember after a leave of absence like that.
Option 1 - start easy. Family med, neuro, or psych. Work hours aren't too demanding and you can get back into the frame of mind of clinical work. If you're interested in neuro or psych (not many mudphuds do family), don't do this option.
Option 2 - start hard. Surgery. You're not going to be writing lengthy patient notes but you will learn a lot about disease entities still (although you learn the most when you're on medicine). However, the hours can be long and you easily get "beaten down". Being "beaten down" is good because whatever comes next doesn't seem as much of a rude awakening and seems much more palatable. Now, if you're going into surgery, don't pick this option.
Overall, if you're interested in a field or two, do not do those rotations first. Why? Cuz you need to perform well and your chances to do so requires some warmup. Plus, you will need letters of recommendation. Unless you make a memorable impression early on in your 3rd year, you will be easily forgotten. If you're interested in a field, it's better to do that rotation sometime in the spring. By that point, you're all warmed up, sufficiently "beaten down", and it is easier to ask for letters (i.e., your letter writers will more likely be able to remember you when you ask for the LORs the summer after your 3rd year when you're applying for residencies).