for me it is
Swiftcast : (resurrection and summon)
Protect : 4 man dungeons / solo
Stoneskin : 4 man dungeons and for thoses occasion better to have tank topped or yourself
Cleric Stance : time to dps a bit
Surecast : almost never use it but I hope one day they add "can move and cast"
But on topic in my opinion stoneskin is a great skill to have as a sch.
Even with a whm in group, in combat if everybody is topped, as a sch you usually don't mind to spend your mana on a few stoneskins to either protect the squishies or reinforce the tank.