I believe that I get the most work done on the stairmaster (stairmill). I tried to google the differences between a cardio session on the stairmaster and treadmill with the results mostly saying both are good.
The stairmaster makes my body mealt. In 20 minutes I can develop a puddle of sweat that has ran down the sides of the machine. It feels hard so I believe it is the hardest/best/most effective.
I have no actual scientific information to back my hypothesis. But as far as gym equipment for cardio I believe it gives the most bang for time spent.
Wondering what y'all think.