DC motors.
Pneumatics are noisy, at least the air compressor and if you PWM the electrical valves it will make you wear headphones. I was in Italy at a contest in 2006 and I saw a guy that built pneumatic legs with the same degrees of freedom as human legs. When they were moving you couldn't stay near because of the prrr-prrr noise coming from the PWM-ed electrical valves... As a funny note, the next day I showed him my version built on the spot with Lego pneumatics, much more silent since I could not use PWM for the mechanical valves... He was knocked over, never knew Lego makes pneumatics and that anyone could build the legs that fast (all it takes is to have lots of Lego parts)!