My thinking is that IMAC requires the most skill to do proficiently.
Pattern requires delicate inputs and no deviation from the line. The goal is to perform the cleanest manuvers at a constant speed, and place the manuvers accordingly
3D requires vectoring the thrust column and knowing how to fly out of a snap in a very light airframe.
IMACequires the precision of pattern combined with a draggy scale airframe and a greater speed variance through the manuvers in addition to placement.

Chris