The only one who will know the answer to that is you. You have to figure out the requirements for your particular robot (needed torque, needed precision, needed speed, allowable weight, etc) and then compare the various options that can fulfill those needs.
As a general rule of thumb, I would suggest that, for a walking biped, pneumatics or hydraulics will likely either be too slow, or too imprecise, to be a good choice, although it does likely depend on the weight class of your robot. Are you talking about a two-kilo tabletop bot, or a two-ton war machine prototype?