Walter:

Right you are. A tiny number of XXIII patrols were made, with some scores (and losses, too, I believe), way too few to be considered strategically significant. Were the Type XXIII's too late to count? Sort of. Were they really midget subs? Not really, but they were mighty small.

I think the XXIII's were too small to be effective - short range, only two torpedoes with no reloads, so I wouldn't count it as a 'best sub' even if we let it into the running.