I don't use fractal designs. They are only useful in special cases, and for the most part are not what I would consider space-efficient.
My fortresses usually have 2-wide main hallways with a 2x2 staircase from bottom to top. I use 3x3 rooms for all dwarves, and only place bedroom furniture in them (1 bed, 2 chests, 1 cabinet, etc.) when needed.
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At the bottom is my central staircase. The bottom half is the mirror image of the top. Below the 4 bedroom blocks are small dining rooms, and above are multiple levels of the same six-room pattern.
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If the main level is placed just below the surface, you get 4 cool looking bedroom towers sticking above your fortress. If you wish, noble bedrooms can be placed on top of these. The design is easy to extend in every direction, and you achieve a high density of 3x3 rooms.