I can definitely distinguish the voice of Gyuri when I first listen to Kara musics. Her voice is so unique! I can also distinguish Jiyoung's voice most of the time because her voice is similar to boa's. Actually now I can distinguish all of them! Hara and Youngji was the hardest because their voice is very similar.
Mamma Mia is not my favorite song, but it's really hooky and cool. I also like the choreography. The choreo of Korean version and Japanese version is slightly different, but I love both. And the lyrics are so good!!
I'm Gyuri biased, but I think Jiyoung's really really photogenic. Her posture and the naturalness is amazing. I especially like her photobook pictures.