what is a better combination
I would say acidic and adrenal implant. Adrenal and invigo would basically give about the same, but adrenal is unremovable. And acidic is on a significantly shorter cd than armor mod.
But don’t forget, acidic coating triggers only against melee attacks and only affects the attacker. Armor mods triggers against any attack and will block the next attack against you, regardless of who is doing the attacking.
And on paper, invigorating speed is equivalent to adrenal implant only if it’s triggered exactly every 10 seconds…but if you have +boon duration, that also makes invigorating speed stronger.
I’m not saying one option is better than the other, just something to think about.
On another note, armor mods AND acidic coating together makes for some fun times…
Astaxanthas (Revenant), Hepaticus (Engineer), Eosinophus (Thief)