Sorry I didn't include which one:

Combat (Normal): Prayer
Combat (Nightmare): Thorns
Combat (Hell): Prayer
Defense (Normal): Defiance
Defense (Nightmare): Holy Freeze
Defense (Hell): Defiance
Offense (Normal): Blessed Aim
Offense (Nightmare): Might
Offense (Hell): Blessed Aim

So Nightmare Defense is Holy Freeze aura. I thought "Infinity" would be good if you are using a lightning charge-up skill.