Mines and torpedoes solve different naval problems

Were sea mines or torpedoes more effective in World War II?

Both were effective in different roles: mines for persistent unattended denial, torpedoes for immediate attacks on chosen targets.

Both mines and torpedoes caused substantial losses for their cost. A mine remains a threat after it has been laid, without requiring the attacker to return for each engagement. A torpedo suits an immediate attack on an opponent. These different purposes complicate comparisons of effectiveness; no ranking by tonnage sunk is supplied, although that measure is raised at the end.