Divine Sunderer

Best
Armor Penetration per legendary is not that amazing, but can help against tanks
Spellblade does 150% of base Attack Damage, only 50% more than Sheen and 50% less than Trinity Force when attacking Turrets specifically, but is stronger on champions
This item has no Attack Speed or Movement Speed, and less Attack Damage than Fiora's other Mythics, but more than makes up for it in the Sheen proc
Early on, this item is a pretty big spike in damage, especially against tanks

Eclipse

Feels Squishy
Armor Penetration per legendary is not good
Fiora does not like lethality items
This item has zero utility and no Health, making Fiora glass cannon, which she can't pull off

Galeforce

Feels Squishy
Movement Speed per legendary feels amazing to chase enemies with
The active is able to hit vitals, which is great, but has a really long cooldown
High Attack Damage is nice and all, but beyond the active, this item lacks utility Fiora doesn't already have
Fiora feels really squishy because this item offers no health, shields, or sustain of any kind

Goredrinker

Viable
Ability Haste per legendary is pretty good
The active heals based on how many enemy champions are in range, which makes it a lot less appealing cause Fiora can't teamfight
This item works much better into many melee enemys in teamfights

Immortal Shieldbow

Feels Squishy
5 Attack Damage and 50 Health is pretty sweet
This item might not have as high Attack Damage as the other Noonquiver items, but it does have Life Steal
The utility that the shield provides is nice, and it gives a decent amount of Attack Damage, but very reliant on being low health

Kraken Slayer

Feels Squishy
Attack Speed per legendary is not that great, honestly
High Attack Damage is nice and all, but Fiora is too glass cannon with this item
The True Damage this item provides is actually not that great considering Fiora already deals tons of true damage naturally with bonus Attack Damage
This item completely lacks utility

Stridebreaker

Viable
Movement Speed per legendary feels amazing to chase enemies with
The active is able to hit vitals, which is great
The active will slow enemies and allows for some juicy vital hits when Lunge is down and one vital is left
The Attack Speed and Movement Speed feels so good

Trinity Force

Viable
Attack Damage, Ability Haste, and Movement Speed per legendary is pretty good
This version of Trinity Force has no mana, but it's better at taking down turrets
Spellblade does 200% of base Attack Damage
The base Attack Damage passive doesn't help Fiora's True Damage, but when Fiora wants to melt turrets, it does a great job

Parry Carry's Fiora Guide