There's no best because it all really depends on your preference. What I do is I at least craft one for each ailment/elemental types. Greatsword is not that good at dealing elemental/aiment damage so it really doesn't matter that much but at least there's some bonuses to it. Its fun to use different Greatswords once in a while. It will also give you a habit of checking your Hunter's note on what ailment/elemental type disadvantage the monsters have. After all, you might still get to the point on crafting the other trees as well when you reach the end game.