ECO friendly is a word up there with organic. How much virgin water and coal burning in a mill is used in the manufacturing process of stainless steel, fossil fuel to transport it ( lets guess where it is made)and a dozen other impacts measured and not.

If you want a onetime buy, longterm unit both are excellent choices.Nalgeen wil have greater insulating abilitysimply based on thicker material. I don't think either will win any contests.