For group debut, I look for great synchronicity and harmonization as looks can be improved later, though I'm not gonna lie that looks are hooks as we're human and easily get attracted to nice looks. This is their new song sans Darlene (now going solo): ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-tKnfovw0kU8.html
Please also check out BINI they are 8 members, female Ppop group debuted 2 years ago and they are known for their vocals (harmonies) and also synchronize dance. Besides form their MV I recommend you to watch their dance practice with live vocals.