Break Blade / Onion Shield

[Maelwys]

IMO it really comes down to the fight mechanics of whatever encounter you're in.

Consider the Twintania fight:

What's a better situation on Death Sentences: reducing damage by 27%, 25% of the time (Allagan).... or reducing damage by 20%, 35% of the time (Onion)?

The amount of Parries will be marginally smaller with the Onion Shield, it's true.
But for every time you lose a parry (24%) you'd be getting a block (20%) and that severe spike of damage would still be mitigated, albeit by a smaller amount.

The above might not be the most "efficient" way of reducing the average damage, but it'd certainly make a healer's life easier if your HP didn't suddenly drop to "danger levels" quite as often. In that kind of fight, a healer would probably not really care whether you mitigated a Death Sentence for 20% or 27% or 24% of the damage, just that some extra mitigation kicked in and left you with enough HP to survive another autoattack after being hit by the Death Sentence.

----------------

For hard fights where one or two spike hits of damage have the potential to kill you, I'm leaning towards the Onion Shield since it would "flatten" the curve and make the amount of damage you take (and the amount of healing you require) more predictable. It makes the Healer's job easier and the fight a little safer.

For hard fights where you're in no danger of dying to spike damage hits and just want to mitigate as much damage as possible over time (Primals?), I'm leaning a little bit more towards the Allagan Shield. Your blocks will kick in for more resistance and you'll get more use out of Parries, but your HP bar will be a bit more spikey. Healer's job is slightly harder but you'll likely take a little less damage over the course of the fight.

Combine this with the fact that the Onion Shield is the only one with a decent DPS stat on it (+11 Critical) so you should really be using it on Trash content over anything else.

TL;DR:
Onion for versus Spike Damage or when you DON'T know your healer.
Allagan/Relic for versus Damage over Time or when you DO know your healer.
Onion for DPS.

That said, I'd not complain if I saw anyone use an Onion shield or an Allagan for any encounter. They're both great options.