This one is super functional for core and hips. If you do it right, with lots of attention, you'll get a real sense of integration between upper and lower body. Start with an imaginary, magic hula hoop. This one is really special. It not only floats in mid air, just where you want, it's also really heavy and massive. It takes a lot of power to get it moving, so you'll have to engage all the fibers around your torso and get your hips into the act. Engage your imagination, settle into your stance and start moving.
You can use whatever stance you like: two feet, one foot or foot and a half. But no matter the stance, get your imagination into the act. Note also that there's a yin and a yang to the movement: there's a push-pull conversation as you move the hoop, just like in any other functional movement.