Male Corrin

This depends on what you will build your Corrin as. Will you keep Yato or go with a different weapon? If you do not care about speed, go with attack to maximize his damage as he will not be able to double unless his build allows him to do so.

Really depends on what you want. A hard hitting or a speedy Corrin.

But IMO go for +spd -res cause corrin does'nt have that much attack to really one shot most units and to compensate for that he needs to double.

But try to level them both up to level 40 and use both of them for a while and decide on which corrin you prefer base on your experience.

Speed is preferred as it is the most versatile stat.