The way we hold a crochet hook—and the reason we find one hook and handhold more comfortable or effective than another—is determined in part by the shape of our hands, the length of our fingers, and muscle memory development. Our lifestyle affects how we use our hands. Someone who swings a hammer every day will hold and use a crochet hook differently from someone who types all day. By being aware of our strengths and weaknesses, we may even be able to prevent repetitive-motion injuries.
Check out the information on the six ways various crocheters hold their hooks on Interweave's post: Know Your Craft: Know Your Hands.