Motorized models force you to keep up with their pace. More expensive models have different programs that add to motivation by encouraging you to keep up with the program. Treadmills benefit the lower body most and can be use for light to heavy aerobic exercise. Some let you increase resistance. You will outgrow a rider as you get into shape.
Riders benefit the whole body for a light to moderate aerobic workout.
Some let you program workouts of varying intensity. Exercise bikes benefit the lower body and are good for light to heavy aerobic exercise. Cross country-ski machines benefit the whole body and are good for a light to heavy aerobic workout. Stair climber benefit the lower body and are good for light to heavy exercise. It s a good overall workout, but if you don t position yourself properly, you can put a strain on knees and back.