It all depends what your fitness goals for the day are:
1) Hi/low- (amazing step combos & blasts from LM, Imax3, KM). This one is my fav. The step and blasts are fun and tough but not dreadful. KM is without a step at the end and you get great simple cardio to finish you off. If you want to burn serious calories, this one rocks!
2) interval blasts + legs (lower body toning & amazing cardio). Personally for me, this one is the hardest. You get the toughest blasts/step combos from Imax3 + the leg conditioning drills from KM
3) Interval circuit (total body toning & cardio combos). This one is fun, but I hate, HATE changing my step height so often. I am very clumsy and fussy with the risers and never change them fast enough (I hate pausing the DVD, then I feel like I am just wasting time, which I do not have much with a toddler).
My only gripe with Hardcore is the changing of risers so often between cycles. For instance she does two cycles of LM, then 2 cycles of IMAX3, then back to LM, ect. I am picky about that, therefor I don't do it that often, only when I want to really work myself hard and have the energy to give 100%. These workouts are probably the toughest Cathe has. Solid intermediate? You are being so humble. You can do these no problem! Very hard on the knee's though, a lot of plyo.
Good luck!!!