[MrForbes]

There are advantages and disadvantages to each. Motors allow precise position control. Pneumatics allow you to put the heavy motor and storage tanks down low on the robot, and use a lightweight cylinder where it is needed, which might help the weight balance. Usually it is much simpler to connect a cylinder (two bolts!) than to rig up a gear/sprocket reduction system for a motor, and you can store energy in the tanks for relatively quick release.

So, as usual, the right choice depends on way too many variables, and you need to evaluate each situation individually.

Notice that none of the considerations I mentioned have anything to do with efficiency! because that is usually not a very important factor in this type of robot design.