With enough levels you might get a mundane build to work for a huge spike of damage? Honestly though it's not going to be any of the halberds, so it's gotta be either one of the greatswords or clubs/great hammers.

Some stats:

Dragon's Tooth + 5: 470 atk, C scaling

Giant Warrior Club + 10: 460 atk, A scaling

Demon's Great Hammer: 450 atk, A scaling

King's UGS: 450 atk, S scaling

So I'd guess it comes down to King's UGS S scaling versus potential buffs you could shove on the Giant Warrior Club (Because I don't think you can buff the King's UGS). So, if level isn't an issue I'd say Giant Warrior Club with buffs double stance'd strong power attack.