Well I'll just go ahead and say what I've always been saying about Rihoko, she is the cutest of the girls. Everything about her just screams kawaii!
Rihoko is my 2nd favortite character after Kaoru and also I'd say she has the 2nd most distinct hair style after Kaoru.
Usually gut feeling would put someone like Sae as the most adorable here but I just find Rihoko to be the one filling that role