Which cardio machine burns the most calories?

In a study published in the Journal of the American Medical Association ( Vol. 275 No. 18, pp. 1382-1450, May 8, 1996) treadmills are the best indoor equipment for fitness training.

The study compared treadmills, Elliptical trainers, stair machines, rowing machines and exercise bikes. Users were asked to use each piece of equipment at a perceived level of intensity. (IE: Easy, medium hard). Measurements were taken to see which piece of equipment caused the user to expend the most energy.