Disney has not yet announced the dates for the Holiday Season. It usually ends somewhere in early January. If I had to guess I would go with Sunday (1/7/18) as the last day of the holiday season because it's ended around that time for the last several years. So my thoughts are based on that guess.
Jan 9 to 12: The Star Wars Half Marathon - The Light Side is scheduled for January 11 to 14, 2018. So there will be fairly significant crowds in the parks starting on Thursday (1/11/18). I do think the first few days, especially the mornings, are likely to be pretty calm in the parks. The last of the holiday season AP blockouts end on 1/8, but most schools go back on Monday the 8th. So it's possible that the crowds will pickup at the point as AP holders come into the parks for the first time since mid-December (especially in the evenings). Assuming the holiday season has ended, it's likely that Haunted Mansion and Jungle Cruise will be down having their holiday overlays removed.
Jan 17 to 19: I haven't yet heard of anything major happening during this time frame. While Monday the 15th is MLK, not many schools seem to have the whole week off (probably because most just went back after winter break). It's likely that some attractions will be down for refurbishment and overlay removal.
This far out, I would probably opt for the second set of dates just because there is no marathon to deal with. If you can wait until more is known about the holiday season, then i would wait.