[Micah]

For all: Luck and resists (elemental and magic) as appropriate to what you're fighting.

Air: Marble armor or something else that will bump their prot value above 20, just in case. They can get away with less if you need the body slot or can't lose the CR, but it's a great choice. Regen if you can spare the slot. A damage shield for chaff killing helps a lot here.

Earth: Stymphalian wings (or flying carpet). These guys are pretty good to go out of the box with regen and invulnerability and summon earth power, so give them a flight item to help their mobility and go to town. The wings will also up their kill rate against small troops since you get 0-enc trample.

Fire: Depends which, Pyri really wants some marble armor due to his 0 base prot, whereas rhuax gets a great boost out of a blood stone for all the good earth magic...both could use some reinvig to combo with phoenix pyre, though rhuax can get that from summon earth power...give pyri a resil amulet if you can. Both get a kick out of flight items as well, although make sure to provide them with escape routes in case they take an unexpected beating, since phoenix pyre probably means they'll get off the field (especially if you give rhuax flight with the wings)

Water: a shield to pimp their defense...the 2 water-only queens are kind of a crappy investment for above-water fighting, as they have no base prot, no regen, and limited buffing magic...they can survive on their high defense against limited opposition, but I'd seriously prefer a golem for most purposes (alchemize for 25 of the 30 pearls, or make some clams instead) Underwater just stack a char shield or stymph wings with resist gear and their high defense and ridiculous regen should be plenty to keep them up...you just want a way to do a lot of damage with them (hence the shield/trample)