What is the best cardio exercise to do at the gym?

[~Poodle~Lover~]

Hey I am going to the gym tomorrow morning and I was told that cardio is the best to gt rid of the fat. They have like treadmills, and stair steppers, elliptical machines, and many many more it is one of the newer 24 hour fitness places what is the best to start on p.s trying to get rid of stomach, thighs,and lose about 15 pounds!