Any of them. Whatever your group needs. If you still bring the DPS heat while spamming it (Chant of Resonance is great for this) you can use Circular Breathing for 3 spirit/second. Otherwise the 10% vitality or 20% all resist or even the life on hit runes are all solid. The big reason you use it is the 50+k absorb shield you can basically constantly have on you and your groupmates. It scales with your globe bonus and healing too so theoretically if you want to go team player build you could get that up to 100k absorb super easy and just sit there, spam that, cyclone, and let your group have ACTUAL fun playing!