Question: Among all the films starring PENELOPE GUINESS, what is the title of the one with the highest rental price per day?
SQL: SELECT T3.title FROM actor AS T1 INNER JOIN film_actor AS T2 ON T1.actor_id = T2.actor_id INNER JOIN film AS T3 ON T2.film_id = T3.film_id WHERE T1.first_name = 'PENELOPE' AND T1.last_name = 'GUINESS' ORDER BY T3.rental_rate / T3.rental_duration DESC LIMIT 1