Precor is a brand name and they make lots of different types of exercise equipment. An elliptical is a TYPE of exercise machine.
What's important in burning the most calories is not the machine, but how hard and how long you work. I can burn essentially the same number of calories by using an elliptical, a stationary bike, a treadmill, by swimming, by walking in my neighborhood, by skipping rope, by dancing, or anything else as long as I do it for the same amount of time at the same intensity. What's more important than the machine you use (if you use one at all) is working in your target heart range. There is a great article on the HeartZones web site that explains this further, check it out:
http://www.heartzones.com/maxfatburn...at_burning.php
That doesn't mean that choosing a method of cardio exercise -- and a machine -- isn't important. I generally dislike riding a stationary bike, so buying one would not be a smart move for me because I wouldn't use it. I like ellipticals, but I have found that different types suit my body MUCH better than others. So, you want an activity you will like well enough to stick with it and do for a sufficient amount of time each workout, and a machine that suits your needs best. Only you can really decide what that is in each case.