Slaying Edge +Spd or Refined Yato on Corrin?

Well, Yato refine gives +2 to all stats. Add the +2 to the weapon refine's +3 for a speed refine, and you're getting a +5 speed boost.

Or you could go with Slaying Edge+ since that doesn't take Divine Dew to refine. lol

The spectrum boost is insane for whom ever you pair him with. Beyond using him for all the stats there are way too many amazing sword units that out do him.

Definitely go for the Refined Yato to give him the unique Spectrum Boost that no other sword unit can give out- probably the only thing about Corrin that sticks out, so yeah, definitely Refined Yato

Slaying edge makes him just like every other sword unit. Yato gets my vote.