I voted for the Halberd. The weapon had many many advantages over contemporary melee ones.
First, the weapon is functional both as a pike and a two-handed axe. The tip is effective at puncturing armor and bringing down cavalry, the axe is capable of cleaving a man in two with relative ease.
Second, the butt-end of the weapon is as useful in combat as the head. But wielding it as a quarterstaff, one can deliver multiple blows in succession, which can knock an enemy off balance, or deflect incoming blows; the shaft itself, being made of wood, is also functional in the defensive role.
Third, range. It has all the benefits above, plus an extra arm's reach to do it with. If being wielded as a two-handed axe, the additional leverage allows greater applied force; if engaging in even closer combat, it can be used as a quarterstaff with a big sharp end, as described above.
All in all, the Halberd was a devastating weapon when correctly used.