Florina IV

Well, the boons are all really good and can work for different builds.

+Res gives her better ploying power.

+Spd is also great when combined with Fury and Darting Stance seal so she can still potentially double without relying on QR.

And attack on effective weapons is never a bad idea.

I'd go with +Spd -Def if it were up to me since I'd wanna keep her Res and Spd intact. Ideally -HP since her weapon makes use of all her stats, -def seems kinda risky but maybe it could work?