Which Caeda IV?

I'd pick +ATK -HP.

+Atk. She could use as much attack as she can get, she's good on speed.

It's very close between +ATK and +SPD (+atk edges it due to superboon imo), but -HP is a much better bane compared to -RES which hurts her ability to run ploys. Also if you wanted to run a distant counter set Caeda to counter mages, you'll want her res intact for that too.

Personally went with +ATK and -HP for my own Caeda.