What cross class abilities should I use as AST?

I currently use protect, stoneskin, swiftcast, and cleric stance. I'm not sure what I should use for my 5th one.

Aero.

/10char

Aero's not very good since malefic II is the same potency and all frontloaded, though it can be cast on the move.

Surecast isn't that useful since you can make your spells instant with lightspeed and not need to worry about being interrupted.

Pick one, it doesn't really matter. Or pick none and save some UI space.

Go with Surecast. It's useful for certain phase transitions to ensure you won't be interrupted when casting Helios, and doesn't require you to burn Lightspeed.

Be like me and level arcanist to 34 pre-heavensward to get eye for an eye for AST, then download the expansion, unlock AST, and proceed to facepalm yourself off a bridge.

The actual answer is surecast, because it's the only one left that may have a practical application somewhere.

Aero or sure cast, matters the encounter

I am currently using aero, before I got gravity I used blizzard II. (Would still come in handy for level sync) I just don't find myself using surecast very often.

Aero for the DPS. Used Surecast in this game like in 2 occasions only and Lightspeed or Swiftcast make up for that ability.

well normally i would want to go for aero, but it has very little total potency, and is just an instant malefic II over time.
so i use surecast, even though i found it useful in situations that i can count on my fingers. if 2 people are dead, the first i will ress with swiftcast, the second with surecast along with lightspeed.