This is a toughie.
I would say depending on whether you enjoy say kickboxing or if you would prefer a mix of things really should factor in on which tape to get.
I bought the dvd of both tapes and do a mix and match of both workoouts. I will do say CM up to the second kickbox section and then go to CK and do either the cardio or the power drills. Others I know do CM with heavy weights as a mix of cardio and weight training.
They are two very good tapes I would find it hard to give you a preference as this always changes.
Couldn't you get both??
Babs