Centres
Bars, then whole centres.
Centres on bigger cubes
Centres are built from bars as wide as the centre, joined row by row: first two opposite centres, then the side centres around them. On the 6x6 and 7x7 the bars are longer and the order matters more, so solvers plan a whole bar at a time. The last two centres share their pieces, and their cases are the L2C sets.