As people have mentioned, it depends on what healer you are.

Generally, the healer melds are looked at subjectively because of their minimal impact. If you dps at all, meld ACC to cap (atm that is at 593) which will require basically all 100% slots unless you use crafted pieces. If not, then you can choose from Crit, PIE, SpS, and Det. Personally, I have PIE till comfortable > Crit > Det > SpS.