Seeing as how he has rarely ever hit 40 in a game, but he has locked down players night after night.....I go with Defense. BTW, yes I know in the Spurs system he won't be going for 40+ on a nightly basis like Kobe, Mike, and RWestbrook. Still, he does have off nights on offense, but he almost never has off nights defensively.
Too bad his Robin is Aldridge.