We went this week a couple years ago stayed onsite at YC. The first 1/2 of the week was great YC was a ghost town, low park crowds, wait times were very reasonable, walk on all the tier 2 type rides. 30 minute-ish waits for headliners not named TSMM or Soarin'. You will notice the crowds start to pickup towards the end of the week. It wil start around Thursday and get heavier and heavier each day as you approach the 20th. If it were us, I would plan our must do's for the first part of the week. We pushed MK until the end of the week and it was crazy busy, we didn't do much the last couple days but try to dodge the crowds. We had ADR's every night and I remember having some long waits even with reservations towards the end of the trip. However NFL had just opened and that definitely contributed to the MK crowd.
Having said all that, I think December is becoming more and more popular and its hard to find a week between TG and Christmas anymore with really low crowds. By "low" I mean 5 or less on 10 point scale (below avg). I still like the 1st week of Dec or the week right before TG the best.