Ok, Stepper, Rower, and Treadmill will burn way more calories then the spinning (think about the amount of muscles your using).
Running will burn the most calories out of any of them, period. However, Stepper is right behind, closely followed by the rower. Stepper is a good alternative to relieve your joints, tendons and ligaments, as is the rower.
However, lets say you are a rower. You will burn more calories rowing then running, becasue you can go faster and longer on the rower. (Although, you will get a benefit from challenging your body, by doing something its not used to).
At the end of the day, you know if your working hard or not. Focus on the exercises that work more body parts. For me I love running, so thats what I do, with a little bit of rowing thrown in there, to get me of my feet a bit.
Finally, make sure you are doing intervals, not long, low intensity. HIIT is much more effective for fat loss
