I prefer the "Chess Tactics" Series, also made by the makers of CT ART
The Chess Tactics Series is
Chess Tactics for Beginners which I have completed for my 7th time
Chess Tactics for Intermediate Players which I purchased two days ago
Chess Tactics for Advanced Players
I personally prefer these... it takes care of all my tactical "needs". While CT. Art covers combinations from 1 or 2 all the way to 8, the Chess Tactics series is more focused on each level i.e., beginner has only 1,2, and 3 move combinations, intermediate has 4, 5, and 6 move combinations etc.
Basically, the difference between these and CT ART (recall that these are both made by the same company) is that the chess tactics series focuses on each skill level much more than CT ART does. Each CD has between 1000 and 1300 puzzles.