I think TJ is much easier than Cathe or Janis. I like that they're dancier, but not everyone will agree.
If you want something tougher, I read at VF that there's new one due out in February, maybe later this month. It's called Kick, Punch, & Jam and it's supposed to be more intense than the others, like a Turbo Kick class. I'm anxiously awaiting reviews on this one.