There is no “official” alignment system forSwords & Wizardry. In some campaigns, the struggle between Law and Chaos is the only supernatural conflict, and Good and Evil are nothing more than personal preferences held by mortals (theSword & Sorcery model). In other campaigns, it is the struggle between Good and Evil that defines where gods and mortals stand in the grand scheme of events (the High Fantasy model).
Some campaigns might contain supernatural factions backing the whole set of Law, Chaos, Good, Evil, Neutrality, or mixtures of the various alignments. These core rules don’t try to tell the Referee how to handle alignment; the Referee is free to use any system he chooses. If you’re playing the game and you want an “unofficial” default, then the players may choose one of three alignments: Law, Chaos, or Neutrality. Most characters will be neutral. The good guys are Lawful, the bad guys are Chaotic, and anyone just trying to achieve fame and fortune is Neutral.