LogFAQs > #913856612

Magic damage in this game is based on Max MP, and you get 2 additional MP overall for choosing the staff with the max for a staff user being 18 MP. Now the thing is there are items you can synth that permanently boost your strength and defense, but no so such thing for getting that 2 additional MP. In short this means Staff can reach the same strength caps as the sword, the same defense caps as the shield, and has a higher magic than either sword or shield can reach. Staff users are always the strongest sora in the long run because of this.

Sword users get 1 extra item slot compared to the staff and Shield gets 2 extra item slots compared to the staff. BUT now the same thing about using items to increase your strength and defense hold true for the shield to. So Shield and Sword have the same strength, defense, and magic caps but Shield gets one additional item slot. Which makes the shield just firmly superior to the sword no matter how miniscule that one slot is.

There is basically no advantage in long run to choosing Sword.