To mimic human anatomy, varying force delivery mechanisms are required. You wouldn't use the same motor architecture for a knee cap that you use for a highly delicate finger joint. Modern humanoids blend Rotary and Linear Actuators to balance power and agility.
Rotary Joints
Rotary actuators utilize spinning electric motors mated tightly to reduction gearboxes (commonly Harmonic drives). These are exceptional for joints that require full-circle continuous rotation or massive pivoting torque under load, such as hips and shoulders.
Linear Pistons
Linear actuators, on the other hand, function exactly like a piston or a hydraulic press, delivering intense push/pull linear motion. You frequently see linear actuators serving as the artificial "Achilles tendon" in modern bipedal ankles, as they provide massive shock absorption directly in-line with the leg structure.