#DBSpoiler Future Trunks' Spirit Sword is much better than Goku's Spirit Bomb. Because not only does it have the Earth's energy in it, rather than just be a giant explosion, all that power is condensed into a weapon which can hit with the force of it repeatedly. Goku's is one shot and done, Trunks' can keep going with it. It is also fast whereas Goku's is slow.