For me it's fairly close between Cara, Brady, and Leah. They all have their own qualities. I think Leah is best at expressing emotion, and Brady great at satire or having fun. Brady has done some really nice videos recently and is really showing her full potential.
But Mary Newman as Cara just pips them for me as a great all rounder. She has had the misfortune of dubious supporting actresses in the Noho House, but she still manages to pull it all together and make the Nohos marginally the most watchable of the four houses. This is confirmed by the viewing figures and it wouldn't have happened if the house was full of Blue or Daniella type actresses.
She's great at introducing vlogs, pulling in the viewer, intelligent commentary, and interaction with her housemates. Plus she has a range of moods and characters which most times she is convincing with. She's had the odd poor video, but considering the range of material and the speed at which it is produced, that's to be expected.
Just a quick aside, Milowent, why weren't the Hiho's included?
For the record I would say Hannah is also sweet and engaging to the viewer. I don't know if she posts her own comments or if they are all still done by Paul or Scott, but she strikes me as the kind of person who might want to engage with her audience.
Kimberly I find very difficult to relate to. She is an OK actress but is too cold to connect with the viewers. I appreciate that may be her personality, but if she is presenting vlogs for a wide audience, I think she has to open her heart in a more convincing fashion.