I think that the sword would win cause it can lunge towards the enemy at a longer range than the hammer can.
Energy Sword because it is a better weapon all around. If you use this correctly you can pwnd Gravity Hammer.
Energy Sword would win, easy. The only exception is in Grifball, the Grav Hammer owns the Sword in Grifball, but that's the only time it does.
If they are going 1v1 head on, the Grav Hammer will win if both weapons are used correctly. If you're talking about a normal match, which gets more kills, usually the sword.
Sword by far, the Hammer lunge kills you more often than not, because it lunges you then swings after you've reached the person. However, the down sides to the sword is the Bulltrue medal (not horrific) and the fact that the hammer can damage in a spherical shape rather than merely with lunges, plus multi player kills with the hammer along with lower battery drain make it more efficient. Overall, if given the choice between hammer and sword - I'd choose sword.
That is because of the low health. Normally, the hammer has to be red to kill, but with low health, you just have to get somewhat close to kill. The sword can't do this and only kills when it makes contact with you. I will take the shotgun over either any day.