I may be biased but Sana! She got to sing in the chorus, her pink hair was iconic and her shot in the MV was so beautiful (the whole MV was but in that shot with her behind all the people passing she looked like a goddess), she also was the one who ended the MV!
special mentions:
Mina she looked lovely in the MV and fit the concept so well, her lines are also my favorite. I just wouldn't say it was her era because she didn't promote with the group and it was such a tough time for her. (I can't wait to see her in the next comeback!)
Nayeon I think the outfits suited her very well and she really stood out to me in stages.
Dahyun because of her iconic rap