Cast iron is a better choice, though it still takes a relatively long time to heat up and cool down. It offers a better nonstick surface. The main problem with cast iron is that when it’s too thin, it is extremely fragile—I’ve seen cast iron woks crack in half when set down too hard. But when made thick enough to be durable, they are extremely cumbersome to lift, which is essential for proper flipping during a stir-fry.
Carbon steel is your best bet. It heats quickly and evenly; it’s highly responsive to burner input; it’s durable and inexpensive; and, when properly cared for, it will end up with a practically nonstick surface. (Read more about why carbon steel is a great cookware material here.) Look for carbon steel woks that are at least 14-gauge—about two millimeters thick—which won’t bend when you press on the sides.
Avoid nonstick woks at all costs. Most nonstick coatings cannot handle the high heat necessary for a proper stir-fry. They start vaporizing, releasing noxious fumes long before they reach the requisite temperature.
