I do have the STS series and got good results but I found I got the better results in less time from doing full body workouts so I would have to say Power Hour and Muscle Max. I believe getting the best results really depends on your body type and finding out what works for you.
On another note, I'm looking forward to Cathe's new DVDs (especially High Reps). They sound as though they are right up my alley.
For me, it was definitely GS and MM. Even more-so than STS. I was amazed by the results I got by alternating those. I liked STS a lot, but had better "visible" results with GS's.