Studying sub results from 1941-1942, the answer is leadership followed by aggression. The corolation for success was highest with leadership, high with aggression, and even higher when you added the 2 togeather. Try to have the sum above 115. Nav skill had no corolation (except that good leadership, and good nav skill ted to come togeather), however I just read somewhere that it influences not getting spotted and ability to get away when spotted, so I guess don't ignore it.
As for corolations with torp usage, there is a decent one for nav skill (higher skill is fewer torps), but a better one with aggression. So if you are concerned with torp expenditure, higher aggression is your friend. That said, the fleet boats don't miss often, and with their high dud rate I want them to shoot more torpedos, but alas, I can't order them to do that.
Stat analysis is fine as far as it goes, but for subs I tend to discount a lot of it as deployment habits can drive your stats all over the place. The most aggressive CO in the game can't hit anything if the player zones him to a dead area. Stats can be directional, but I wouldn't become too enamored.
Also, I don't think (correct me if wrong) your analyses include use of the deck gun. In the early war, after the first upgrade cycle, this can become a fairly significant tool, especially on unescorted TFs when playing the AI. In my experience playing the AI aggressive USN COs tend to use the deck gun more often than low-aggression. This results in more sinkings, but also more submarine damage and potentially losses. Sometimes the most aggressive CO is not the best one for the job. Very aggressive COs also sometimes drive into minefields while in pursuit.
Just a few things to consider.
< Message edited by Bullwinkle58 -- 8/27/2013 1:14:13 PM >