I finished STS around the middle of November and then I started P90X.
My opinion on these workouts are:
STS has more variety in it. The workouts are fun and each phase does a little something different to your body. It tests your strengths, especially. You can do any cardio workout you want on off days and now with STS Shock Cardio, you can easily add those in to the rotation. I never got tired doing this workout and looked forward to each and every one of them. I had a lot of fun with this.
P90X, although a very good workout program, gets boring after you do about 5 to 6 weeks into it. The cardio workouts (two of them) are the same throughout the entire 12 week rotation. This got really mundane for me. This rotation goes back to the classic workouts people did before machines. Lots of pullups, chins, pushups, etc. I liked each different weight training workout, though, and those didn't seem to get old. However, my body can only take so many pullups and that is what made me stop after my 6th week. Tony is a fabulous coach and his workouts are fun, but I think he could have done a few more cardio workouts and at least one more leg workout. There is only 1 leg workout with this rotation.
If your question is which is a better rotation, STS wins hands down. No questions in my mind. Cathe is a genious and she put this rotation together like a true pro. I got more results from STS, but in my case that isn't fair to say because I never finished P90X. Although I think that speaks for itself as well.