I guess it boils down to your interpretation of "crowded." Last year, we went the first week of October. While crowds did pick up by the Columbus Day weekend, we felt that, overall, the park was LESS crowded than our previous stay the first week of December. And we'd read that the first week of December was supposed to be one of the least crowded weeks of the year. We used Fastpass as needed, but were able to do everything we wanted to do, plus some extras in all of the parks.
Our fall break week has shifted for next year, and we'll be going Oct. 6-14. We'll be beginning our trip at Columbus Day weekend, rather than ending it. Therefore, I expect a few more people then. We plan to use Fastpass and also to enjoy our resort more.
The nice thing about October is that it's still warm enough to swim, but it's not sweltering. We loved it and are thrilled to be going back next Oct.
Have fun planning!
Christy