The way I do SoS is int>crit>spirit>haste>mastery but that is just the way I've learned works best with my play style, more often than not there isnt a bread and butter build for healing priests. (Some will flame me for my build I'm sure). Imo it's just about trying what feels best, give it some time and teel your GM that's what you are doing.
Edit: also depends on how good you are at using your mana cds / if you have Veiled Shadows, because then you can afford to have less spirit.