With Rainbow things are a bit tricky because they are not just one of the most balanced groups in hotness, but also in talent. Jisook, Hyunyoung, and Seungah are all main vocalists. Woori is the rapper, which often also entitles her to spoken lines at the start of songs. With those roles, they all get put up front a lot but it's not like the mains in SNSD. Rather, each song they do tends to focus on two of them, so depending on the promotion, you'll get a different idea of who is the main person. Regardless of this, Jisook and Hyunyoung are the two powerhouse vocalists.
Jaekyung has strong vocals as well but her title is no joke as she primarily leads the charisma of the group. The fanservice is especially cranked up for performances other than music shows. No Eul and Yoonhye are the only ones who can be considered support members, but they are also considered visuals. I can understand that for No Eul, especially since her dancing is extra sexy, but I don't really see how Yoonhye is particularly cute. She was actually fairly frightening (dem terrifying eyes) in Korean promotions for A but has been better lately and is cuter in selcas.
