Hi,
Increasing muscle size is mostly determined by genetics and muscle fiber type, but the truth is, in order to increase both size and strength, one must apply the principle of overload. That is, doing more work than the body is normally accustomed to doing.
You must choose a weight that will allow for momentary muscle fatige within the desired repetition scheme, whether it be the high or low end of the rep range. This applies to all types of strength training be it pyramid, superset, or straight sets. Most women simply will not use heavy enough weights, and so us instructors must find other creative ways to trick them into achieving muscle failure, such as higher rep schemes and higher set schemes (which is really what pyrmaiding is about).
I often read on the forums that some people got better results with lighter weight and more reps, but no one seems to consider the fact that the reason this approach worked was because the muscle was brought to fatigue, or failure, by the end of the rep set with the lighter weight (overload), not necessarily because a lighter weight was chosen. Were these people really bringing the muscle to failure by the end of their shorter sets by choosing a heavy enough weight to accomplish the goal?
My advice is to not worry about which type of training is best to increase mass, but remembering to always apply the overload principle within your desired rep scheme, and change the approach every few weeks or so for optimum results.
-Roe