This is relative because every player has different starting skills. But assuming that all the skills are at an equal level, I would always start with OD because defense is one of THE MOST important skills in basketball. If you suck at defense, then you're gonna get no where.
But if passing is like as low as awful/inept, then I would train passing first, maybe to respectable or so, because OD single position training requires a player to play as a PG, and obviously you wouldn't want an awful passer as your PG (unless it's a scrimmage etc).