Hmm, whilst I would never intentionally argue with the lovely and illustrious LauraMax, I do personally like Ab Hits, particularly the plank work. This isn't to say CoreMax isn't a good set of workouts, too, it's just I prefer stuff that doesn't make me feel like I've been hanging from my neck for several hours. :7
Marie
(PS: You will eventually own both, so it probably doesn't matter which you start with.)