Healing melds..

[Fevelle]

I'm a main WHM, so for my main healing equips I meld Piety and SPS - piety directly raises my MP management tools since Assize is % based, and SpS makes for good regen ticks and fast healing for when I have to deal with Cintamani-like raid damage alone. Also, with a big MP pull and some spell speed, you'll be the a machine Holy bomber in roulettes.

Or just meld acc in everything.

Main Healers don't need the extra piety

I don't know how good your group is, but oh boy do I need that extra Piety to get some more Raises going... Piety is probably the best stat for healers in progression parties.