Clearly most subs sunk should determine the winner.
In case of a tie, most damage given should be the first tiebreaker.
If there is still a tie, least damage received.
If there is still a tie, call it a draw.
I agree with this scoring system. Subs sunk is most important, followed by damage given/taken.
However, I would *not* use scoring to determine the winner. Rather, I'd score to determine 2 finalists and have them battle it out in one last death-or-glory match.