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.
URW Game Encyclopedia description
The official URW in-game encyclopedia (accessed by the key) describes the spear thusly:
The spear has a long wooden shaft and blade specially designed for melee combat.