Although this questions comes up almost weekly, it just made me think why I use the developers that I use. One point not regarded before here in this thread is toxicity. That's why I would avoid today developers containing Hydroquinone, and the best known is D-76. Hydroquinone can cause severe allergics and is supposed to be cancerogenic.
So if low toxicity counts, my choices would be developers containing ascorbate instead, either Xtol or self made developers with Metol or Phenidon and Vit-C. The probably most harmless developer that can compete with regular developers is self made Caffenol-C.