I'm not Cathe
however, I asked her that question a few weeks ago and here is her response:
"Thats a tough question, hmmm, I would have to say IMAX 2 (especially intervals 5 through 10)for step intensity. It's funny how on Imax 2 you finish interval 4 thinking "yeah, this is tough but I thought it would be tougher and then..... But I also love the variety of Boot Camp and how it gradually sneaks up and bites you."
I know that with Cathe in Florida, this might get missed.