The stat weights appear to depend entirely on the stance. Spell speed has a huge merit to those who diurnal stance while Det is more beneficial to noct. All other stats are preferential.

Heres what I have found successful: (lets ignore piety cause thats honestly your filler stat)
Diurnal: SS=Det=crit (Det is slightly better)

Reason: Diurnal stance is known for their dps capability. They can push out dps numbers superior to noct stance.
Spell speed with a difference of 40 spell speed i noticed about 10 HP more per heal over time tick. It also has more of an impact on the actual cast times. Yay more dps!
Crit rate is awesome! With heal over time you'll see some ticks go up by 600! usually 1 happens each time.

Noct stance: i tested spell speed. It does like literally nothing but increase the speed by maybe 1/50'th of a second for 100 spell speed. its garbage. Dont use it. Det=crit>>>>>ss is good way to go.