* Cast iron. Durable, naturally non-stick and able to withstand higher temperatures than other non-stick materials, it has the added advantage of browning meat and other foods better than PTFE-coated pans. Not surprisingly, cast-iron cookware also leaches bioavailable iron into food, providing additional amounts of this essential nutrient (J Nutr, 1998; 128: 855-9). However, for those with iron-absorption problems (haemochromatosis) or certain types of cancer, excess iron should be avoided.
On the downside, they are heavy and not dishwasher-safe.
* Stainless steel. Again, stainless steel browns foods better than non-stick surfaces. This is the most economical choice. However, stainless steel isn't good at conducting heat, so it normally also contains a small amount of other metals such as iron, chromium or nickel, which can leach into your food if the pan is scratched. Having said this, the levels of nickel and other leached metals is very low compared with the levels of these metals already in the food itself (Contact Dermatitis, 1998; 38: 305-10).
Nickel is implicated in numerous health problems, notably, allergic contact dermatitis, so if you're sensitive to nickel, you'd do better to switch to cookware not made of stainless steel (Arch Environ Contam Toxicol, 1992; 23: 211-5).
Alternatively, you may well avoid this problem by purchasing copper-bottomed pans for better heat conduction.
* Glass. Glass cookware is inert, or non-reactive (making it probably the safest of all), and dishwasher-safe. In one study, there were significantly lower amounts of nickel and chromium in the foods cooked in glass saucepans compared with stainless steel (Contact Dermatitis, 1998; 38: 305-10).
* Aluminium and anodised aluminium are not recommended. Aluminium is inexpensive and an excellent heat conductor, but it is also toxic (it affects the bones, and accumulates in liver and brain tissue) and readily migrates from containers to foods, especially into acidic and salty foods (Ann Univ Mariae Curie Sklodowska [Med], 2004; 59: 411-6; Food Addit Contam, 1996; 13: 767-74).
Harsh chemicals are used to make anodised aluminium, which seals off aluminium - but only until you scratch the surface. And it's definitely not dishwasher-friendly.
* Be cautious of the new, hybrid metals such as titanium until they are proven to be made with chemicals that are not toxic.