Definitely Fairy Physiology, Elf Physiology is second to it.
Elf Physiology grant me "Enhanced Condition" which is far better than peak Human Condition the highest mental and physical condition that a human can reach. Add to that they are immortal race with their biological-immortality.
Fairy Physiology grant even better feats than Elf Physiology, they have "Magic". Since Fairy Physiology divided into three groups and assuming I can choose which one I will be (Ethereal Faeries without doubt) I can be Fairy with godlike power, even if I can't choose any and I will be normal /standard Fairy I will not lose much as they have their magic and Shapeshifting as Common Powers in Fairy race.