The spear is the basic, definitive weapon within its category.  A little stronger and heavier than the javelin, this two-handed weapon's effectiveness in combat and it's chance to hit when thrown are modified by the Spear skill.

While the northern spear, the Kaumolais spear* and the ango all have slightly higher Point ratings, none of these seem to be available in anything other than standard quality.  Therefore, a masterwork spear is likely to be the 'best' spear in terms of damage potential.

Blunt Edge Point Attack Bonus Defense Bonus Weight Value
4 N/A 7 Decent Little 5 lbs 344

The spear has a long wooden shaft and blade specially designed for melee combat. 

-Game Encyclopedia

* I have found multiple fine Kaumolais spears, but no masterworks.