Surcouf and the M class share a failed cruiser-submarine idea

Who had the better cruiser submarine, France with Surcouf or Britain with the M class?

Neither; both were terrible attempts to make an appealing but unworkable idea succeed.

The question compares France's large gun-armed Surcouf with Britain's M-class cruiser submarines. Both designs receive a strongly unfavorable judgment, with neither selected as better. The underlying idea has an attraction on paper. The difficulty is turning the mixed surface-warship and submarine roles into a vessel that works well in practice.