Both are really great. CTX is great because it has short/intense cardio sessions ending with weight training for one body part. It also includes Leaner Legs which is a great lower body workout that can be used as an add-on or a short workout on it's own. If I remeber correctly, there is also an ab workout as well although I don't remember what it's like. It's really a versatile series.
The Body Blast series is one that I use more often. I love Step Blast as well as KPC and STP. Supersets is great but not all that difficult as is push/pull. When I ordered it, I included the Time Saver DVD and I ended up never using it because the other DVD's included some really great premixes. So my opinion is, if you want workouts with shorter cardio sessions and intense, one body part weight training, then go with CTX. If you want really great and longer cardio sessions with total body workouts, then go with Body Blast.
AND, if you can order both, do so!! They're both worth owning!!
cArolyn