well due to the way blizzard have made high lvl priest stuff you little choice but to go for +healing stuff, cause of the 5 sec rule you better with + mana reg than spitit to regen your mana, and due to the way blizzard are going with respec to there high lvl dungons were fights last a long time you then you need better mana regen as you never have enought int(size you your mana pool) to last a whole fight
now since the high lvl chants cost so much, and for the forseeable future iam not going to get a better staff than what i have then the +55 healing is the best choice for me, given that over time i plan to upgrade all my stuff to + healling + mana regen