Everyone talks about how swords are the only weapons that require skill and that polearms and axes did not, this is a hateful lie. There is a reason armies had axe and spear units but not sword units, the sword was more of a symbol of office than anything else. Its main advantage lay in the fact that it could be sheathed and was tiny allowing you to go wherever you needed and have it with you.
Now that I am through ranting against sword suprmemacists I have to go with the Halberd. It was pretty much deemed the most effective weapon ever, useful against armored, mounted and unarmored foes and other than siege engines and buildings what else is there? If I couldn't get a halberd I would go for a Battle Axe or Glaive.
Also, your using not building siege engine option is missing balistae, everyone knows there is nothing better than smashing through a formation with an arrow the size of a tree.