For me I think it's Seungyeon.
Because she's adorable and smiling, and I bet the people would warmly accept her.
I also think Gyuri would do well.
Because she has so much confidence in her, and that confidence would help her be successful.
Edit.
Is it me, or I find it amusing that I joined January, the person above me in February, then after her, joined in March, and the other after her joined April. And by adding the dates they joined, 5+10+5 = 20, which was the date I joined. lol! This is such a coincidence! xD