I'd rate AzuDaioh as one of the top 5 High School/Slice of Life anime ever. Each of the character is so likable. Azuma-san (Azuma Kiyohiko) did a great job depicting high school like it really is.
My favorite characters in the series would be - Chiyo-chan (for the eternal optimist in her), Tomo (you hardly see more lively character than her), Osaka (her absentmindedness is contagious), Kaorin (sigh! her unrequited feeling for Sakaki) and not to forget Yukari-sensei!!!