There are a lot of ways to do cardio but there are only 3 that are mainly used in a gym setting. Those are treadmill, elliptical, and stair-master. If I was going to rate the most effective to the least effective, I would have to say it would go in this following order. I personally use stair-master to burn off body fat. I use treadmill to give me change of pace. On the days where my energy is low, I gravitate towards the elliptical. Cardio is a great way to stay in shape even if you do not lift weights. It is also good for your heart because it opens up a lot of different blood vessels to flow into your heart. If you want to burn fat, you should keep your heart rate low so this way your not losing muscle. But if your going only for cardio, you could do fast pace but this way you will lose weight but also lose muscle.