The longest lines I saw on my December trip were on Main Street USA and at the Partners Statue. As Mountdew1 said, there are multiple photographers along Main Street, but all of them had a small line of 3-5 individuals, couples, or groups. The lines at the Partners statue are confusing, because people seem to forget the concept "wait your turn" and jump in whenever they want to.
There were also shorter lines of 1-3 individuals, couples, or groups at the photographers at the Epcot entrance plaza (because of the Christmas topiaries), and the walkway from Future World to World Showcase (because of the Lights of Winter and the Christmas tree).
And the many photographers in the Streets of America at DHS always had at least one person, couple, or group queued up to get their pics taken with the Osborne Lights.
I saw no lines at any of the photographers in Animal Kingdom.
Once the Christmas decorations come down, many of these lines will evaporate.