Safest cooking device I know, Willow stick and a cooking fire in the back yard. After that, cast iron has nothing in or on it that can hurt you, unless you get your spouse angry at you.
Seriously, aluminum is safe, as are ceramic coated pans. If used with moderate heat, even teflon is safe. Copper has to be tinned as copper can leach into foods and can cause heavy metal poisoning over time.
Of course there is much controversy about the safety of one type of cookware over another. My grandparents used cast iron and lived into their late 80's. I've been using cast iron, aluminum, stainless steel, borosilicate glass, tempered glass, and for very specific purposes, teflon for all of my adult life. I'm turning 60 years of age very soon.
I don't believe you will find one, absolute answer as there are advantages, and disadvantages to each kind of cookware.
But beware, leaded anything is bad. Just ask the ancient Romans who used lead utensils, goblets, and such things. Ever wonder why Nero was crazy, look at all the lead in his life.
(I know you already know this. I was just being goofy. Must have picked a little loco weed from my garden.
Seeeeeeya; Chief Longwind of the North