Which mage Eirika?

+Spd for blade tome.
+Atk is good for her weapon.

Tbh, I’d go with +Atk. If you’re putting her in a horse emblem I’d go with Atk. She gets +7 Spd when she initiates attack on foes with 100% hp and another 6 from horse buffs. That’s really fast for a horse unit.

I'd say that +spd -def would be the best one, +spd is always apretiated on a mage, Bladetome or not.
-res is better than -def as it will increase her bulk, most of the character of the game will hit her def (DC users and dragons) and with so few mages in the meta -res won't ruin her matchups while -def will lead her to get oneshotted in many others, her res isn't high enought to use ploys anyway so you lose less with a -res rather than a -def