Aluminium is normally found as an alloy rather than as a pure metal. Its light weight and excellent heat conductivity once made it a popular choice for all kinds of cookware. It has the disadvantage of being soft and therefore easily dented. Also, being a very reactive metal, it is easily attacked when used to cook highly acidic foods such as rhubarb and many kinds of fruit. Unfortunately, the anodised surface if applied is not self-repairing so that, if scratched, any colouring is permanently damaged.
Stainless steel is made from iron, carbon and chromium.
Often nickel is added to improve the corrosion resistance and formability. It's stainless steel, not just on the outside but all the way through, and resists attack from a wide range of acidic materials. It is hygienic. It can be kept shiny and clean with little effort. Stainless steel products last a lifetime.