There’s a reason crowd calendars don’t agree…because they have little to no accuracy value.
We haven’t gone the second week of December, but have done Thanksgiving twice…’15 and ’17. Also did Christmas both of those years. Everyone wants to see WDW at the holidays…for good reason. So expect it to be busy. From folks I’ve talked to, early to mid-December is less crowded than the actual week of Thanksgiving and the days after for sure, but not a ghost town by any stretch.
No offense to a new poster, but I’m not sure why PP above would say that the rides would have less things “wrong” with them at Thanksgiving. Doesn’t make sense to me. And WDW is in full Xmas bloom by Thanksgiving, so no issue there either.