+Atk or +Spd Eir?

+atk if ur gonna use her in a flier emblem/want to use heavy blade on her.

+spd is otherwise better

Both are really good (no supers but eh) personally I'd probably aim for Spd to help with more doubles since she already has 37 spd, but her Atk is kinda low at 32 so Atk would probably help her the most since her weapon gives both Atk and Spd it's honestly all up to you

Keep in mind that while above 50% HP she effectively has 41 speed. She should be able to double most threats with that much speed so I'd opt for boosting her attack so she can kill them too.