I agree with Rennies with most of the stats.
Accuracy for Savage Raids
Get Piety to a good point
Crit. Hit is good (It is an RNG-based stat though, with a diminishing return the higher it gets)
Determination is meh (I think it's about 100 Det for around +15HP on 400 potency heals)

For where I differ:
With Spellspeed, I view it like Piety, get it to a point where you can cast comfortably (the HoT/DoT return isn't that amazing though)

As for Vit, Vit is only going to be useful in Savage Raiding and maybe new EX primals/Trials first come out. Once you are geared up, it isn't really needed unless you keep taking too much damage.

As for when you should be using Noct sect vs Diurnal, it really depends on the content and your other healer. If you have a SCH in the party, go Diurnal. With WHM, you can go either but Noct's shields complements it more. If it's double AST, you'll need to work it out with them.

I my opinion, Diurnal's +5% attack speed boost and place-and-leave HoT's (that can be extended) are better geared for a more offensive/off-healer play-style, while Noct's +10% healing boost and place when needed shields is better geared for a more defensive/main-healer style.