It's tough for me to pick a series b/c I like various workouts from all the series. If I was stranded on an island with a fully equipped air conditioned workout room and could only take one Cathe series, I would probably pick the Intensity Series b/c it has cardio, circuits, strength, and endurance. Well, maybe the Body Blast series b/c it has so many premix options, fun music, and it would have more cardio options as well as circuits and strength.