It's true, Ayaka's voice is much more powerful than Hikki's. Hikki's voice is kinda...shaky sometimes. And sometimes she has difficulty hitting certain high notes, which her voice starts thin when hitting those high notes. xD So Ayaka is better at delivering vocal performances. Like Outlaw said, she is a way better singer and sounds EXACTLY identical to the studio version. Very talented woman, she writes her lyrics and composes her own music. I think she did an acapella with Kobukuro. And her songs are great, though sometimes they kinda follow the same formula. I could listen to her lives all day...

Have you heard her cover of Ozaki Yutaka's 'I Love You'? o_o Holy crap. It's amazing. I enjoyed Mika's and Hikki's covers also. But Mika's kinda sounds bored [though the gospel flavor for the album version of the cover is brilliant. =D] and Hikki's voice is a bit too shaky. While Ayaka...she sang that song so beautifully. =D

But I love them both equally the same. ^-^

And her songs don't have hip hop beats...o_o It's mostly acoustic, upbeat, and funky. =D