1. Jessica
2. Sunny
3. Taeyeon
4. Seohyun
5. Tiffany
6. Yuri
7. Sooyoung
8. Hyoyeon
9. YoonA

just really love Jessica's & Sunny's high & cute voice...
and don't like YoonA's voice...

1.Taeyeon
2.Jessica
3.Seohyun
4.Tiffany
5.Sunny
6.Yuri
7.Yoona
8.Sooyoung
9.Hyoyeon
I think Sunny and Yoona improved

I think...

1. Taeyeon
2. Sunny
3. Seohyun
4. Tiffany
5. Sooyoung
6. Yuri
7. Hyoyeon
8. Yoona
9. Jessica (everybody loves it but for me it's whiny and annoying, no offense)