Well, I think it's best to have the "Hit ALL enemies" skills first because there is literally no benefit to reducing the number of enemies before these fire off. After that though, the "hit 2 enemies" skills occasionally will be worse if they go before single target, like in that specific example given by Miu, but generally speaking having the single target girls last is most frequently optimal because for many pests it doesn't matter, but when you come to boss + adds, it's MUCH better if the single target girl is left with no option but to hit the boss lol.

Me, I need to rework my helper squad a tad, I think, since I'm mixing in Toad Lily. I have BB -> Anemone -> Flowering Peach -> Cyrtanthus -> Cepha atm, which leaves me with Hit All -> Hit Random -> Single x3, but Toad Lily is Hit All, so she'll go after BB and before Anemone.