there are a couple of videos on youtube ranking their vocals but most of them are years ago, so it would also be nice to watch something that’s updated, tho check them out if you want. :) tho in my opinion (i have no vocal expertise whatsoever, i’m just an avid listener), i would agree that Jiwon and Hayoung are their top vocalists, i even thought back then that both of them were main vocals. it’s also nice to recognize Seoyeon - she is actually their main rapper, but she usually ranks high in the vocal rankings i’ve watched. she has a really good singing voice!
