Hasn't this thread already been done?
Anyway...
What is your favourite Film?
Screaming
Who is your favourite Character?
Either Pepe (Peter Butterworth) in Abroad, Anna Vooshka (Elke Sommer) in Behind, Sergeant Bung (Harry H Corbett) in Screaming, Bungdit Din (Bernard Bresslaw) in Up the Khyber, or Doctor Frederick Carver (Kenneth Williams) in Again Doctor.
Probably Sgt. Bung.
Who is your favourite Actor?
Jim Dale
Who is your favourite Actress?
Hattie Jacques
What is your favourite Scene?
Too many to choose from - but probably the scene in Screaming when Sergeant Bung (Harry H Corbett), transformed into a werewolf, returns home to his wife (Joan Sims) and she doesn't notice the difference.
What is your favourite Line?
"Fakir off!"
Which of the series regulars do you think were underrated?
Peter Gilmore
(Under-used in the films IMO. He made 11 Carry On films but he's classed as a "Carry On Irregular" on the Carry On Line website, while Frankie Howerd, who only made 2 Carry On films, is classed as part of the "Carry On Team")
Edit.
I agree with Sidney above that Peter Butterworth was underrated as well - he was often under-used in the films, but when he was given a descent part such as in Screaming and Abroad he was a star!