Interesting subject and such contradictory statements. First: according to my experience, everything with dark background is very bad for my eyes, unless I work in total darkness. But you shouldn't work in darkness anyway, just turn the lamp on.
Second: for (my) eyes feels best the backround color which I would describe "light neutral gray with slight greenish tone". BUT: especially these colors are very different from one monitor to another (with same RGB value), for example these are "guibg" colors from my two computers' schemes: guibg = #E2E2D8
on one pc and guibg = #E6EDD8
on another. Despite the colors look very similar they have different values. So honestly, there is only one way to make it "good for your eyes" - just pick some good scheme and finetune the colors, especially this background color is important imho. Also you can set several schemes with bg color adopted to outer lighting conditions. So if you see a description like "this color scheme is very good for eyes", it's sort of bulls*it, since it really depends. But I'd certainly advise to avoid any dark schemes.