Hey there, I play holy priest, raiding 10 content with a gear level of 354. Agreed with Slutty, from the above post about crit, as a holy priests its really not needed (reforged/gem/enchanted) if there is some on an item then great! . But unlike the post above, I have actually gone for more of a balance with haste and mastery, If im honest its upto you, some think that the mastery is great some dont, haste is good when you have alot of it. If you are raiding then whats your raid comp? It may help in choosing you what to reforge etc.
From xp im keeping them balanced, and doing competitive Healing. In conclusion Haste/Mastery > Crit. Hope this helps