copper is "attacked" by acid foods. so for the last couple hundred years copper cookware was 'tinned'
more recently a stainless steel lining process was perfected.
un-lined, un-tinned copper is still used extensively in the confectionery world.
>dangerous
yup. and stainless leaches chromium and nickel into food, cast iron leaches iron into food, aluminum will make you go batty, glazed pieces leach all kinds of elements and metals into food, 'heat proof glass' aka the 'old' Pyrex leaches boron, etc and so on. it does not matter what you pick, somewhere on the Internet you will find a nutcase with new-age (non)science telling you how bad it is.
tinned copper will require 'retinning' after some period of use - 4-5 years to 20-30 years, depends on who is stiring the pot with what. quality retinning can be hard to find, and can cost as much as the copperware did originally.
I have the stainless steel lined; even though I like "old fashioned" - I'd not recommend the tinned interiors.
copper is best suited for gas cooktops - electric coils heat and cool so slowly you will not realize the benefits of having copper as a heat conductor - solid copper does not work on induction.
Bourgeat and Mauviel are likely the "leading brands" - I would not think about a hammered finish/construction except for purely decorative uses.
if you check out their wares, one could reach a suspicion it's all made in the same place/factory/whatever - sure look alike...