I've stayed at Shady Knoll, it's okay, we liked it better then Atlantic Oaks which we only drove through. Think I'd call all of them and see if you can even get reservations. It can be slim pickins the holiday weekend which may narrow your choices. I also like Scussett but it is all the way at one end of the cape, we usually prefer a more central location and use Nickerson as we don't care about hookups. If I remember correctly, Scussett was redone not long ago so it may well have changed since I stayed there.
The weekend AFTER the holiday is the Wellfleet Oyster Fest which is a good time albeit crowded.
As was mentioned, a lot closes after Columbus day.