Re-reading my post, I don't think I clarified myself well 
Because Ice Armor reduces all damage (vis-a-vis Heart of Despair, which only reduces Physical Damage), isn't it better to use Ice Armor + (persistent ice spell of choice)? That's been my conclusion by comparing both approaches, but I haven't done eiher extensive or systematic comparisons, so I could be wrong about the mechanics.
The ice armor passive is buggy at best. I greatly prefer heart of despair, myself. And after having coined a sarebaas build around heart of despair and other damage resistant passives, I'm very confident that that staff reduces ALL damage, not just physical.
If it's only protecting you against physical damage then I wonder if your promotions or equipped gear have anything to do with the equation. For example, if you had really high con and low willpower, the staff would look like it protects against physical damage, but you would still take more damage from magic (willpower protects against magic). Also note that spirit damage bypasses typical resistances, and I'm unsure if this is true of the staff.
To your question though: Ice armor can be used effectively with pretty much all ice spells except ice mine. Ice mine is a toss up, because the ability seems to bug out even if you leave the area and come back. Winter's grasp, blizzard, and other chilling effects seem to trigger ice armor reliably. But the benefit of heart of despair is that it never wears off--even after death (it's a visual bug that causes your armor to disappear but the buffs are still there).
So, in short, I prefer Heart of Despair because it's more reliable, but ice armor can be made to work by taking abilities other than ice mine.