Here's a bit of physics that will help you make a good choice. Metals are all conductors of both electricity and heat. Glass and ceramics are insulators against both electricity and heat (and yes there are exceptions). Metals, glass and ceramics, and all cooking vessels also have a property called thermal mass.
Here's how it works. Some metals are better conductors of heat than others. That is, when heat is applied to the metal, a good heat conducting metal will be able to absorb more of that heat in a given period of time, and transfer it to other objects touching it through a property called conduction. So, a good heat conductor is also a good heat radiator or source.
Steel and iron are relatively poor heat conductors as far as metals go. And because of this, they tend to get hot where the heat source touches them. That heat energy will spread to the surounding metal, but slowly. This creates uneven temperatures accross the cooking surface, usually reffered to as hot and cold or cool spots. Of course this makes food preperation difficult as some portions of the food will cook faster than other portions.
This property can actually be an advantage in certain types of cooking. A good example is with stir-fries, and is especially evident in a carbon-steel wok. Typically, the surface touched by the flame is where the cooking takes place. And because of the wok shape, it allows food that is done to be moved from the hot bottom to the cooler sides. This makes room on the bottom for the cook to prepare more food. When all of the ingredients are cooked for the dish, everything is combined. Because the sides are warm, even hot, that food located on teh wok sides is already realitively warm and is readily mixed into the hotter food.
Cast iron is another pan that conducts heat poorly. But it is also thick, massive. It takes substantial energy to get it hot. That energy is stored in the molecular vibrations of the metal. When foods are added to the hot pan, it transfers that stored energy to the food in a continuous manner. This makes cast iron great for cooking things like meat that has to be seared and browned. The pan will transfer sufficient energy, and in a controlled manner, to keep oils hot for frying, or pancakes browning evenly. Though the pan has hot spots, over time (called preheating), the cooking surface temperature will even out, creating a great cooking surface. And believe it or not, that black color that develops over time, helps the metal absorb heat faster.
Stainless steel pans are made of thinner metal and develop fairly dramatic hot spots. As all materials expand and contract in physical size when heated and cooled, this can even cause permanent warping of the cooking surface as some areas of the cooking surface expand more than others. Rapid expansion and contractions of cast-iron can cause it to crack or even explode. This is why you never place a hot cast iron pan into very cold water. Teh iron is brittle and the great pressures cause by the rapidly cooling outer metal skin can cause catastrophic failure of the metal.
In stainless steel cookware, to help eliminate the hot spots and provide a uniformly heated cooking surface, more conductive metals, such as aluminum and copper are used to distribute the heat evenly to all parts of the steel cooking surface. This is accomplished by the heat source raising the temperature of the steel where the heat concentration is greatest. This heat is quickly absorbed by the highly conductive aluminum or copper that touches the steel. That heat rapidly spreads in the more conductive sandwiched metal, which in turn transfers the energy, by conduction, evenly to all of the cooking surface. In effect, it takes the high conentration of the heat at the source and distributes it accross the pan surface.
So you can see that with stainless steel pans using the multy-ply disks on the bottom, or a direct layer of copper or aluminum on the bottom, the pan will heat evenly accross the bottom cooking surface while the less condutive stainless steel on the pan sides will be more resistant to heat absorption. In some of my stainless pans, I have seen the bottom bow upward slightly as the pan bottom expanded faster than did the side, which had no highly conductive metal touching it. When that pan later cooled to a uniform temperature, the bottom again became flat as it contracted.
With pans like All Clad, where the aluminum or copper is sandwiched throughout the pan, the sides will be heated by the heat jsut as the bottom is. This is useful for boiling liquids, making stews or soups, or any other cooking chore where you might want heat to come at the food from all sides. It's not very helpful if you want to saute mushrooms, or fry an egg.
I mentioned glass and ceramics. The question you might ask is; if they are heat insulators, why do we cook with them? The answer is simple. They are not perfect insulators and do heat up as energy is applied to them, albeit more slowly than do metals. But they have enormous thermal mass per unit volume, and tend to distribute heat very evenly to foods. They are usually used where slow and moist cooking techniques are required, or when you want to present heat evely from all directions to a food, such as with baked beans, casseroles, stuffings, pot roasts, etc. But even they have limitations. They don't heat quickly and so require more energy and time to get up to temperature. And square or rectangular casserole dishes tend to concentrate heat at the corners, creating hot spots that can burn foods before the entire dish is completely done.
So what do we get from all of this? Simply that the many pans, pots, and cooking vessles vary in performance characteristics. Some are better for one thing, while others are more suited to something else. To say that one type of pan is best, is at best, ludricous, and at worst, just plain wrong. Figure out what kind of cooking you do most, that is, what techniques you prefer. Then you will be ready to choose the proper cookware for you.
Seeeeeeya; Goodweed of the North