Currently holding multiple rank1 on healing as Guardian Druid on some fights and the heirloom trinket is a must if you want to be invincible. With the legendary ring i can put up 1.3 mil shields against demons, so i won't even flinch.
https://www.warcraftlogs.com/ranking...&spec=Guardian
Imo, Anzu is BiS, followed by the heirloom, if you fancy a huge shield with a 1 min CD, shortly followed by Kilrogg's trinket. Seed is pretty poop as it's not really a life-saver, as it doesn't reduce a lot from big hits (the most i've seen is like 27k), where the Kilrogg trinket for ex can absorb a lot (you're at 1 mil hp, you get hit for 1 mil, but the trinket takes you to 20%, effectively healing you for 200k exactly when you need it), not to mention the haste is good for lowering the GCD and CD of Mangle and Frenzied Regen (especially if going with 4-set). Right now i'm running Anzu + Kilrogg after i've ranked a bit on healing.