Which Ayra?

I would say do the -atk +spd. You don’t want her to lose to much defense from -def, plus the speed boon just works really well even with -atk, especially since she has her specialized Astra. I’m also running -atk + spd and it works wonders

Ayra cares about SPD, and little else. The other one can be merged, or used as Swift Sparrow fodder, as it is one of the best A Slot skill in the game.

The first Ayra is best choice to go with. Her naturally high Speed means her Regnal Astral does more damage. If she can achieve over 50 Speed, then it more than makes up for some loss of Attack.

And secondly, it's best to merge whatever spare Ayra onto the first one. But if you are in dire need of Swift Sparrow fodder, you can definitely save her for someone who needs that.