Barbecue grills come in a number of different types of material. If you are looking for a grill that provides you with the best overall cooking surface, cast iron is certainly worth considering. Porcelain-coated, stainless and other grid types are also available; cast iron grates come in the middle of the price range.
Cast iron is one of the best metals around for cookware because it is durable. It is heavy, strong and can take a pounding. If you use your grill frequently and don't want to worry about it getting banged up and damaged quickly, cast iron is a good choice. Porcelain chips much more easily and stainless steel simply doesn't have the same kind of strength that cast iron grills offer.
One of the best things about grilling with cast iron is that it distributes heat evenly across the cooking surface. Grills of various kinds, especially those that use charcoal, generate extremely uneven heat. This results in food that doesn't cook evenly. Hot spots on a grill make it very difficult to get perfect steaks every time, but a cast iron grill that distributes heat better makes it easier to get the results you want.
Some people worry that food will stick to cast iron grills, but this isn't the case. The key to a cast iron grill as a non-stick surface is seasoning the grill properly before you use it. This means rubbing shortening or lard over the entire grill carefully, then burning the grill at high heat for roughly ten minutes. After you cook, leave the food residue on the grill until you're ready to use the grill again. Clean it just before you use it, rather than right after. If food starts to stick, clean everything off and re-season the grill.
Cast iron is a much better conductor of heat than stainless steel. This means that when compared to stainless grates, the grill on a cast iron barbecue will work much more efficiently, even at low heat. To get the grates on stainless steel hot you need to use much more heat than you do with cast iron. Cast iron is also more efficient, because the metal holds on to the heat for longer than steel grates.