Usually if the crowds are bad enough to cause capacity closures, MK goes first. Then after that, it depends. Usually Epcot is the last just because of the size of the park itself (that was my choice to go to the last time I spent Christmas Day at WDW, and I found the crowd to be heavy but manageable). As the parks stand right now, I would say AK would hit capacity before DHS, just because there is more at AK to draw a crowd - but DHS may seem more crowded because there is less to do. Once Star Wars opens at DHS, I would expect DHS and MK to be kind of neck and neck in the capacity races.