Do you use natural light or studio light? Is one better than the other?

Neither.

Natural light offers different challenges than studio lighting because you are dependent upon good weather, and the quality of light changes as the sun moves across the sky. Sometimes you get really magical lighting but it only lasts for a little while. Studio lighting is easier to control and not "worse" than natural light, but if you don't know what you are doing, it can look dated and have that studio look. I shoot with both natural and studio, sometimes both at the same time. But when we use studio lighting, we use it in a way that makes the light look like natural light and not at all like it was shot in a studio. With either natural light or studio lighting, great care must be made to have the light approach the subject from angles that will flatter the subject. With overhead lighting, which you get from the sky, it is easy to lose the energy in the eyes, having them come out somewhat dead and in shadow. The light must catch the eyes in a way that makes the person seem vibrant and full of energy. If you control the light adequately, you also see color and detail in the eye that can astonish. It's all about angles.

A lot of photographers I have seen that claim natural light is the only light you could possibly use, are actually failing to control the light adequately. The result is the person simply doesn't look their best. I shoot on location and in the studio, but always take great care to see that the eyes are full of energy and are being hit with good light. The question is not whether natural or studio light is better, the question is whether the photographer can control the light and make you look your best.