My personal experience is that it's great to mix things up, to avoid injury and increase enjoyment
When I lost 30 pounds some time ago, I think it was all through steady state stuff. I definitely got my heart rate up there, but I was doing a lot of step, hi/lo, and kickboxing. No metabolic, HIIT, circuits, insert-new-trend here. Although I do love my HIIT and metabolic workouts, steady state is like a comfortable friend, waiting to meet my achy joints and bad mood with open arms.