I have stated this in other threads, but it is worth repeating. Almost all of my 13 or so trips from Vermont have been during the Presidents Day timeframe.
It can be crowded but not elbow to elbow crowded. I stated that I like a certain number of people in the parks for a couple of reasons. Number one is that it makes the parks seem alive and teeming with excitement. Number two, the fact that there are more people in the parks means that MOST of the attractions are up and running (CoP & Timekeeper the most notable exceptions).
I have been there when it was more crowded and I frankly didn't like it, too much humanity. That week is just right. Not to many, not to few. In short, in my opinion, the best time to go...period!