ditto on elliptical- it is just too bouncy for me.

I like to use the treadmill at a high incline (15%)- then I can walk slowly but it is still good cardio. Also the incline helps me lean just a tad forward which helps my posture. The stairmaster works similarly, i just walk slowly in both instances...but if the level is set right on both machines I can get good cardio without jostling anything too much or losing good postural form. I also find the handles in both cases to be good for resting the hands on...i.e., i can do treadmill easier than i can walk down the street----