I would say November and December were about equal for me. If you can only do one, just pick one and try to stay on top of replying to invites ASAP; I think those dates are about equally easy/difficult to get.
I also only took one month off during interview season. One strategy that I used was to take an elective with flexible scheduling hours during the other big interview month. For example, in my case I did a Pedi EM elective, and since weekend shifts are essentially the same as any other shift I just put my "days off" in the middle of the week and used them for interviews. That wound up working out very well for me.
Beyond that, while it's the job of the administration to take a "hard line" and say you can only miss X days during a rotation, the truth of the matter is that most of my friends who wound up being forced to take rotations that should theoretically be "inflexible" found a way to work it out with their team. The residents, for the most part, remember what it was like to go through the application season a couple of years ago, and as long as my friends worked hard while they were there and made a good-faith effort to schedule their interviews for the time they had off, if something unavoidable came up the team would generally find a way to make it work.