I think my favorite look for the sisters was the soft, dark green outfits they wore from "Redemption, Part II" to "Firsborn". There's just something about it that's so alluring. Part of me wishes they'd kept it for their final appearance in Generations.
You just think it was their final appearance. Actually, unbeknownst to many, they were secretly beamed off the ship before the Bird-of-Prey was destroyed. I am still waiting for their return.