I have had the older ones (thicker metal, don't know what kind of metal...) and the newer thinner metal one. Mine are Mirro's. I like the thicker ones. The first time I cooked beans in the thinner one they burned and I can still see the outline in the bottom. I was using a glass top electric stove and that may be what caused this. Both work just fine as far as the 'pressure' cooking part goes. My thinner one came from Wal-mart.
Good luck on your search.