I picked Mei, since she's the only one of the set who I didn't have yet.
An Alpinia dupe was tempting though. Already have an extra equipment slot on Sakura (for her personal earrings), an equipment slot on Cactace doesn't make much of a difference (she's mostly powerful on her special, her regular damage is a bit lackluster), while I leave Black Baccara benched since I simply don't like her artstyle.