Condi Duration Reduction or Condi Clear
If your strictly front line, with a lot of HP and armor, then the condi duration would probably be better overall. You can take some passive condi clear traits, or the smite condition if you have Valor (which most people do) to help get you out of trouble if anything lingers after you fire Purity.
Trooper’s is better for mid line and second wave since it can clean up after the AOE bombs and get the front line mobile again. But because its burst clearing, it doesn’t work well inside the bombs as those will reapply instantly after you clear.
If you’re in an organized group consider hoelbrak, when you recover in a group and empower makes your might all that much longer while still getting some benefit from condi duration reduction and a more offensive stat set.