Swords have their own separate category of enchantment. With six enchantments available, there is plenty of room for non-overlap, especially since only the first three are exclusive to one another. Unfortunately, two of those three are very restrictive in what they help you out against ,and may be exactly -not- what you are looking for. In the end, though, swords are easier to get ‘the right combination’ on than armor is.
Knockback can be hard to get along with- try to avoid hitting things on edges, or you may find yourself diving for exp when you use this sword. Fire Aspect is very fun, letting you set things on fire in the process of hitting them and making it easy to get cooked meat from animals, but keep in mind that catching fire happens -after- the attack damage, so if you killed the animal with the attack and not the fire, the cooking doesn’t happen. Finally, Looting will not get you more Wool, Spider Eyes, or Chicken (raw or cooked).
Sharpness (Max level V): Adds 1-3 hit points of damage to each hit per level, randomly determined on hit. Cannot coexist with Smite or Bane of Arthropods.
Smite (Max level V): Adds 1-4 hit points of damage to each hit against a Skeleton, Zombie, or Zombie Pigman per level, randomly determined on hit. Cannot coexist with Sharpness or Bane of Arthropods.
Bane of Arthropods (Max level V): Adds 1-4 hit points of damage to each hit against a Spider, Cave Spider, or Silverfish per level, randomly determined on hit. Cannot coexist with Sharpness or Smite.
Knockback (Max level II): Increases the knockback distance on your hits with this sword. This knockback is overridden by or overrides the knockback from your running attacks, the longer distance of the two taking effect.
Fire Aspect (Max level II): When you hit an animal or monster with this sword, the target catches fire. A higher level of enchantment means a longer fire.
Looting (Max level III): Increases the number of each item dropped by animals or monsters you kill with this sword by a number equal to the enchantment level. Also, the chance of getting a rare drop increases, with a larger increase per level of the enchantment.