VersaClimber is the best cardio workout that I have ever had! This is coming from a guy who who was an elite level swimmer and h2o polo player for over a decade. 30 minutes on that machine, and I'm spent!
Some weeks I feel strong and can do more - so I run more. Some weeks I am spent and can barely drag myself out of bed - so I spend more time taking it easier on the elliptical or stationary bike. Some weeks I need the motivation of a group class, so I take more classes.