as a group... i would have to say their vocals. i wonder if they get one on one with an experienced professional vocal coach because they can sing but sometimes it's a lilttle bit too raw you knw? the power is there, they just need to smooth it out and fine tune it.
individually..
nicole.. i love her to bits but sometimes her rapping is not up to par with "rap" i think she's loosing her flow.. im not sure if that makes sense but if DSP wants her to rap in english then she needs to be able to flow with the words not just speak random words. and honestly, someone give the girl lyrics that are coherently stringed together.. not just multiple one line phrases bunched up together.
seungyeon.. well im a little bias. haha. she's an all around good performer.
hara.. vocals. vocals. vocals. albeit she's come a good distance since rock u days. hara honey needs to sing with more power to match her stage presence! but if not then atleast turn her mic a little higher then the rest because she naturally has a soft low voice.
jiyoung.. ahh maknae needs to improve on her emotions/facial expressions when on stage. whenever she sings she mostly has a cute smile on and sometimes the music doesnt translate with it.
gyuri.. i think dancing... she just needs to go all out when she dances... like nicole, ham, and hara... sometimes it looks like she's holding back or maybe it's just because she's dancing next to power houses, either way i think she needs to practice more... maybe not dancing per say but "letting go"