The Stainless, Aluminum, and LTD lines are almost exactly the same. All three are aluminum bodied with a stainless cooking surface. This is what makes "Clad" pans expensive, the bonding process which yields a thick even-heating aluminum body with a thin but durable non-reactive stainless cooking surface. This simple design is what the MC2 line is... aluminum body and stainless lining - nothing more. The exterior is simply brushed for an industrial-like matte finish (as opposed to a shiny polished finish). Raw aluminum scratches easy anyways, so polishing it would be kinda foolish.
The LTD line uses an electrolytic process which causes the exterior of that aluminum body to become ultra-hard (through oxidation). The LTD line is essentially the MC2 line with an extremely durable exterior surface, but is still just "2-Ply" which theoretically provides better heat transfer.
The stainless line adds an extra layer of stainless to the outside of the pot that some people like (primarily for looks). This adds another layer, making it "3-Ply", but the aluminum body still accounts for a solid 80%+ of the thickness. Theoretically it would actually heat less-evenly than the MC2/LTD, but I'm sure you wouldn't be able to tell the difference outside a laboratory.
The "copper-core" adds a thin layer of copper sandwiched between aluminum layers, and then layered inside and out with stainless. I'm sure they function just fine, but I question their purpose, especially all the layers and inherent interstitial flaws.
If you want a good copper-clad pan, Mauviel makes 'em. They are kinda like MC2 pans being "2-Ply", but with a solid copper body rather than aluminum. The exterior of the copper is also polished rather than brushed. But prices are way out there, like $500 for an 8qt pot. I'm just jealous because I don't have them.
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