Let me start off my saying that this is all based on observation not fact. If 你 have any 问题 leave a comment. There is no 显示 that tests their English and see how well it is and its no secret that they are taught what to say on shows 或者 interviews, so 熊 with me.
Ok, now the only ones left that actually speak English pretty good are "S trio".
Sunny-she is confidence when she speaks English,has a slight accent when she speaks, reads English novels
earliest found English:
link Sooyoung- She needs 更多 confidence when she speak English, has a slight accent when she speaks, has an English speaking roommate
earliest English:
link Seohyun- Se has confidence when she speaks English, has a slight accent when she speaks, studies English
earliest English:
link I personally think Seohyun Sunny and Sooyoung rank after Tiffany and Jessica.
Latest English from all of them:
link