I like the CTX series, but if you want tough workouts, go for the KPC+PH, etc. package you're thinking of getting. I think you'll be happier overall with it if you want tough workouts.
Get CTX as your next purchase for the Leaner Legs, All Abs, and the short (yet high intensity) cardio programs.
To be honest, though, you can't really go wrong with either set...but I just bought CTX and was a little disappointed with the Upper Body Split (it wasn't what I thought it would be - too fast-paced - I felt like I wasn't in control, even though I was using lighter weights - I prefer slow-count weight work), and a couple of the cardio workouts look like they require more room than what I've got to exercise in. I haven't done 10-10-10 and Kickbox, yet, because I'm going to have to make the moves really condensed to be able to fit the workouts into the space I have. So, if you don't have a lot of space, you may want to consider this.
On the other hand, I'm looking forward to Leaner Legs. I haven't done it, yet, but previewed it and it looks killer! I will definitely feel this workout the next day! And, the All Abs section is fant-AB-ulous! I've already noticed an improvement in my abs and it's only been a couple of weeks. Step & Intervals gets a whole lot accomplished as far as cardio goes, even though it's only a 30-minute workout! I can't believe how challenging it is for such a comparatively short workout! I felt the power-15's in my arms the day after I did this workout the first time.
So, there. I hope my mini-review of CTX helped you a bit in your decision!