Why the proc relic (which only buffs absorb, not shield) and not the triggerable shield/absorb pve relic?
I'm thinking PvP Defense relic and triggerable PvE Defense relic for my Guardian.
The Absorb proc relic grants 113 Endurance as well as 455 Absorb Rating for 6 seconds every 20 seconds. It is a very useful relic, the clicky relic just adds one more button to mash to the already complicated guardian rotation and PVP Relic is better anyway. In some particular fights like Kephess Absorb Relic shines, while in fights with multitude of swaps like Toth Zorn or Firebrand Stormcaller (a lot of moving) a Static Defense PVP relic will be much better.
It is safe to say that BiS for Guardian Tank is to get 2 PVP Imperiling Serenity Relics and also get Dread Guard Shield Amplification relic for specific fights that are more static nevertheless hard hitting.