I know they used to give small elemental stat buffs in the past, but I was thinking in something else. What about this:
Halone: +50% experience from defeating enemies outside instances
Menphina: +5% experience gain if bonded partner is in your party; Eternity Ring cooldown reduced by 50%.
Thaliak: +10% movement speed if you're wet (doesn't work inside instances); gains an action that allows to run over water
Nymeia: Can set an extra Free Aetherite Destination; Return cooldown is reduced by 50%
Llymlaen: Reveals Aether Currents and Treasure Chests in the map; +100% experience from discovering a new location
Oschon: Retainer Ventures and Field Exploration are 25% faster, +5% mount speed in all zones
Byregot: 35 extra inventory slots
Rhalgr: +25% experience from PVP
Azeyma: Immune to fall damage; can spend 1 Phoenix Down to revive yourself (doesn't work inside instances);
Nald'Thal: Market Board fee reduced by 50%; sells items to NPCs for double the price; Gil gained by Treasure Hunts increased by 10%;
Nophica: Experience gain from Well Fed increased to 4%; gardening is 25% faster
Which one would you pick?