I'll be unsurprising and go for the frontliner: Suzuki Airi.
My personal order in C-ute is
Airi >Chissa & Maimi >>>>>>>Nakky & Mai
To be frank, I find C-ute pretty boring.
In general, their songs are generic idol fare or dance style. Thankfully, their recent ones have been slightly more exciting generic idol fare.
Personality wise, Airi's your basic girl next door, and so is Maimi with a bit more genki. Chissa's more my way or the highway tomboyish. Nakky's the emo type. I have no idea what Mai's personality is ever since she and Chissa stopped playing pranks. Erika was another one I didn't get.
At least Kanna was interesting. A charming lack of confidence, yet happy to get her hands on any of the other girls. Sad that she had to leave.
As a plus, C-ute always appealed to me as the professional group in H!P. Overall, they're the best dancers as a group. Individually, they don't have the best dancers in H!P, but their worst dancers far outdo the worst in the other groups. I wasn't surprised that one of their recent concerts was a Dance Special.
Of H!P's flagship groups, I enjoy watching their concert performances the most. Their concert MCs generally are made up of sketches, which are hit-and-miss. But their song performances - yeah, it's good stuff.
Tsunku also seems to be pushing their presence online - what with Chissa's Odotte Mita series, their live streaming concerts, the activeness of their YouTube channel.