Question in the title. Pulled the two above Kagero and looking to fodder off one for the carrot. Originally was thinking of keeping the neutral, but after doing some theorycrafting, not so sure.
It depends on what you want to do with her.
If you decide to keep her default weapon, the Neutral IV is better because the loss in Atk really hurts her offensive capabilities should she need to attack.
If you want to run the -Blade tome set, then you want the +Spd IV because the the bonuses from the weapon make up for the -3 Atk deficit.
I misread that as Catria. My bad! [And I feel kinda stupid right now. :( ]
Anyway, I think that +Spd is better overall because her Lethal Carrot will add an extra 10 damage when the Special activates, and she can pull it off very often if she doubles, which is easy to set up with the Hone/Goad Flier buffs, +Spd refine, etc.
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