I'm looking at this in terms of a few points:
1. Once you become dependent on an avoidance trinket to reach X (uncrittable, block cap, etc.), it becomes very difficult to move to all stamina trinkets. I ran into this in BC. This has made me hesitant to move to an avoidance trinket yet, but...
2. This isn't an either/or case. You can, to an extent, treat your trinket slots like gems and enchants. Right now, I have
Thick Autumn's Glow in some slots to work up to block cap. A person using an avoidance trinket might choose to use
Enduring Forest Emerald instead.
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So look at the options:
Defense/avoidance:
Repelling Charge
Valor Medal of the First War
Stamina:
Essence of Gossamer
Sonic Booster
Both:
Figurine - Monarch Crab
Indestructible Alchemist's Stone
The avoidance trinkets both offer the same (point wise) amount of avoidance, plus your choice of an on-use emergency avoidance boost, or an on-use emergency effective health boost.
The best stamina trinket, the Essence of Gossamer, compares to either avoidance trinket at a ratio of 1.32:1 for stamina:defense (or stamina:dodge). That ratio favors defense/dodge, since the gem ratio is 1.5:1. Comparing the stamina and avoidance trinkets alone, it would be better for me to switch all my pure defense gems to defense/stamina, then use the defense trinket with my choice of avoidance or effective health. The next-best stamina trinket (from engineering) is a distant second and, given it's unneeded threat effect, not worth using. (Yes, I use it now.)
That leaves the combo trinkets. Both are profession-only items, so these aren't even an option for many people. The monarch crab can be gemmed up to 105 stamina and 8 defense rating (using blue gems), which at 1.5:1 is the equivalent of 117 stamina. It's almost, but not quite, as good as the pure avoidance trinkets. It's on-use effect is the same - almost, but not quite, as good as the on-use avoidance.
For the alchemist's stone, the 75 stamina and 50 dodge rating is the equivalent of 150 stamina at 1.5:1, making this the best overall trinket in terms of stamina + avoidance. However, it's on-use effect may be the least good. The improved effect of potions can turn that potion into a better emergency button, but it's still
one emergency button, whereas the avoidance trinkets provide an additional button to go along with a potion.
In Summary
I'm a proponent of stamina trinkets. I started this post to prove this to myself and others. But I've just convinced myself I was wrong. If I were an alchemist, I'd consider using the Alchemist's Stone, but only because I have a bad habit of forgetting on-use item effects, and I don't like becoming reliant on one anyway. Other than that, the avoidance trinkets are the "best" two options, especially since I can make up part of the stamina by switching to combo defense/stamina gems on my gear.
I would certainly keep, and carry, both an Essence of Gossamer and a Sonic Booster, for fights where a majority of the incoming damage is magic-based, because in those cases a maximum-stamina set is the best possible effective health. (Also switch to these when being inspected for inclusion in a PuG.) I will never allow myself to become dependent on the trinket defense to be uncrittable.
But for an all-around tanking set, using both defense/avoidance trinkets is a good choice. In a fight with an even mix of magic and melee damage, I'd use the Essence of Gossamer along with the Repelling Charge, offering me a large amount of stamina plus an on-use stamina boost, plus a large amount of avoidance.
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Paladin of the Argent Dawn since 2004
Trinkets with panic buttons are fun and bring much needed extra interactivity to the game and healers DO notice when such trinkets are used.