+ atk or + spd eirika

I'd say attack

She desperately needs help in attack as her damage is just so low

Her atk is pretty low and she has a superboon in atk, but i still think that spd works better for her, as this will help more in both offense and defence. With a boon in atk you will deal 4 more dmg but with a boon in speed you may get more followups and receive less

Speed is better most of the time. You'll do more damage if you double and you'll also be safer if you're harder to double yourself.

Speed is better imo. You can always run TA if you want her to check some units, but her speed is crucial for her to survive some encounters with faster nukes.