Any dense, or detailed texture that is used on large brush faces, like the big interior walls of the last room. For large walls, you should use textures which are not visually noisy. If you are worried about having large spaces of the same texture, you can use lighting and occasional bits of detail to break them up. For example, the lightmaps of upper sections of walls, and ceilings, will have shading on them because of point_spotlight and stuff, and shadows from bits of the structure, such as beams and pillars.