Which British carrier best fulfilled its intended role?

Which British carrier did best at the role it was designed to perform during the Second World War?

Ark Royal and the Illustrious class are strong candidates, but Unicorn excelled as the fleet's aviation-support backstop.

The comparison separates combat fame from success in a ship's intended role. Ark Royal and the Illustrious class are strong candidates because their designs supported important fleet operations. Unicorn's aviation workshops, stores, and command capacity sustained other carriers. Acting as the fleet's backstop was less glamorous than launching a famous strike, but it made Unicorn exceptionally effective at the support role for which she was built.