I don't know how the engine picks the "Best" defender, if it weights only OD for outside or OD+ID, and ID for Inside or a combo of ID/SB/OD and perhaps rebounding?
I think its a combination of all defensive skills but I'd find it hard to believe that if you have a player with significantly higher OD he wouldn't be regarded as your best outside defender.
Your analysis of the box Ds seems sound to me though.
The one thing I try to remember to point out is that if you read the description of the defense (At least in the official American English, though I haven't compared with proper English just yet) is that it always refers to the "fifth" defender, not the best defender:
Box-and-One defenses: Four players play in a zone defense protecting the basket while the fifth player plays a man-to-man defense guarding the best offensive player on the other team. This prevents him from scoring as much. There are two types of box-and-one defenses:
Inside Box-and-One: The fifth defender focuses on the opponent's best inside scorer. Normal pace.
Outside Box-and-One: The fifth defender focuses on the opponent's best outside scorer. Normal pace.
So at least according to the rules, the player being defended is specified as being the best inside/outside scorer, but nowhere is it stated that it's the best inside/outside/combined defender on him. My assumption based on a very small sample size from ages ago was that the man defender would be the best defender of that type among the three players not in that primary defensive role, to wit:
outside box and one: PG and SG are the top of the box, the best outside defender among the SF/PF/C is the man guy, the other two are the bottom of the box
inside box and one: PF/C at bottom of box, best ID among PG/SG/SF as the man guy, other two at the top of the box.
But that's just my wild guess and as likely to be wrong as right.