Some interesting views here.
I have to agree the Cross Trainer is the best for myself as it burns a greater number of calories than any of the other machines.
I thought about the fact that maybe it was too easy but I now guage myself on the amount I sweat.
I have found that on the Cross Trainer I get a good deal of sweat going faster than if I was doing say the Treadmill or the Cycle for the same period of time at the same heart rate.
So if you ask me, sweat is a great indicator on how hard your working yourself. Although that may sound rediculous its working out for me