I like Imax2 the most of the 4 workouts, but CW is so easy I never ever use it, except for the abs workout. I do like the CW sequences on the Terminators, and sometimes I use the CW all step premix as a cardio warmup to a leg workout.
The StepBlast workout is really fun and reasonably tough. I also use the premixes. I don't do SJP as is, but I do the all cardio premix sometimes, and I like the SJP weight work in the Timesaver workouts.
So, I'm not really answering your question am I? x(
Truthfully, I wish you could choose Imax2 and StepBlast, and skip the other two.
But if I were you, knowing what I know, I would get IMax2 just because it is so great, and the BlastMania premix is such a wonderful HIIT workout, and the abs in CW is good. But either way is good. I have a mild mild preference for the IMax2/CW one.