Someone may beat me to this, but here is a brief run down:
HSTA has all cardio sessions on a high step (set at 8").
HSC features some high step cardio (on a 6" step) and some floor cardio.
HSTA offers 5 cycles of the following: cardio, leg press, lower body work, compound movement, upper body working same body part that was worked in the compound movement.
HSC offers 5 cycles of the following: cardio, lower body, upper body, sometimes more lower body, then some more upper body - HSC has a 'less structured' format - but it moves a lot faster and I really like that.
HSTA offers no ab work
HSC offers about a six min. ab segment just before the final stretch.
HSTA offers SIX rounds of leg presses (holding one dumbbell in your hands)
HSC offers 3 of them (two with the band, one with overhead presses using light dumbbells).
HSTA groups all the chest work together, bicep work together, etc.
HSC does not do this; you'll do push ups in one cycle and then pec flies during a different cycle.
HSTA offers about 11 total min. of cardio.
HSC offers about 6 total min. of cardio.
HSTA has tougher upper body work and some interesting moves like one-armed tricep dips.
HSC offers some interesting moves as well, including a lot of Dyna-band work.
HSTA is my favorite of the two - because it leaves me feeling more "worked out" than HSC
HSC, however, has more of a fun factor and I LOVE the music.
I'd recommend both.