I would be inclined to guess that the January dates will be busier. The holiday AP blockouts end on Jan 2 (Signature), 3 (Deluxe), and 4 (SoCal and SoCal Select), which means those groups of AP holders are likely to return to the parks that week to see the holiday decorations and offerings one last time before the Holiday season ends (likely sometime after the 7th). On the plus side, there is a pretty good chance that the parks will still be in the Holiday mode, meaning the decorations and entertainment will still be offered, along with the attractions with holiday overlays (e.g., HMH, IaSWH, Jingle Cruise, etc.).