They are all good, and I'd have a hard time choosing just 1 or two, so instead of specific recommendations, here are some things to consider that might help you decide:
>CTX Series (With some caveats: the weight work is superb, Leaner Legs is one of Cathe's best lower body workouts....but I can't think of many of her lower=body workouts that aren't good!; the concept is excellent. However, there is a lot of step--even Cathe now recommends doing step only 2-3 times a week, and there are 4 CTX workouts that contain it--and a LOT of impact to be done on consecutive days. If you can, or don't need to, modify, then that's no problem. Also, some of the cardio is a bit of a space hog---like doing two-steps to the side,then turning, and continuing to do two steps in the same direction. The music is good--instrumental--but is very repetitive from one workout to another, and also repeats some of what is in CK. Cathe is at her best as an instructor here---very energetic, without being over-the-top, and motivating.)
>Slow and Heavy Series (A unique series in Cathe's repertoire. I love the upper body workouts, but not the lower---my knee does NOT like slow lunges...at least last time I tried. Some people find it tedious because it is so slow, but I like that about it. It's the only workout of Cathe's that I feel gives sufficient recovery time between sets, and that's actually minimal--1 minute--compared to what is recommended. I also like that you can play with the count--I often do 5-up/3-down --4 up/4 down for shoulders--because the 2-down seems a bit fast compared to the 6 up, and it takes it closer to the 2-seconds up/4-seconds down recommended in weight training books.)
>Power Hour, Body Max, MIS (A good variety of workouts. PH is a body-pump type endurance workout. It usually gives me DOMS every time I do it. BMax---I refuse to abbreviate it as "BM"!, LOL!--is superb. A challenging blend of cardio, cardio/weight circuits and upper body work. A classic. MIS is a good full-body weight workout. I haven't done it for quite a while, but there may be some moves that might need to be modified to be safer.)
>Pure Strength (I'm just rediscovering this one, and so far, I wonder why I haven't done it for so long---maybe too many "reps" being described as "sets", LOL! A very straight-forward split routine that is not as frenetically paced as some of Cathe's later workouts---like the Pyramids, which are too 'hurry, hurry' for me when done as-is. Simple, effective. Some moves that are not in many other workouts, but are good ones (like lying cross-body extensions===which Cathe calls 'kickbacks', but they aren't). There are some moves that could lead to injury if you aren't well versed in exercise safety. For example, on tricep bench presses, Cathe has you place the weights on the floor from a lying-on-the-step position between sets, then pick them back up again while still lying. This puts the shoulder in a compromised position and could cause injury.)
>Circuit Max/Cardio Kicks (CM is a fun, effective, athletic cardio/weight circuit. CK is a kickbox-flavore hi-lo workout. CK grew on me---I prefer more 'kickboxy' workout like KPC--but I grew to like it. There are some moves that take a bit of space. CK is from the beginning of Cathe's kickboxing training, and her form leaves something to be desired--one reason I had a hard time liking it at first--but there is a lot of energy in the workout, and it's fun. The extra-long warm-up (11-12 minutes) transitions well into the workout itself, and is nice to use as a warm-up to weight workouts.
