Are you more interested in cardio or strength, or both?
PS is known for being one of the slowest, heaviest lifting tapes available, and it's all lifting. There's no cardio in it at all, so you'd have to tack on your own cardio or do it on alternate days.
CTX has a short, but INTENSE cardio section followed by weights for one body part. The weights used here are lighter than on PS, but they go on forever, with hardly any rest!
So, for many people, they find that they build mass and strength with PS, and lean down and gain endurance with CTX. This is a HUGE generalization of course, you won't really know how YOUR BODY will respond till you try it.
CTX cardio does move fast and with little breakdown, but if you don't mind using your rewind button, you can learn it. And it is so versatile - you can mix and match the toning sections, cardio sections, or what-have-you. And the music is SOOO awesome and motivating.
My inclination would be to say get CTX because of its versatility - but really you'll eventually want both

have fun!
Sophie