Thanx to all the replies. they are certainly insightful.

So according to all answers, swords are still better b/c they have higher attack and moral stats.

However, I must ask why are polearms weaker against ranged missiles??

Also, people seem to forget polearms, spears and pikes generally have higher charge stats than swords. You can see this when comparing cavalry with sword and cavalry with spear...(the latter one always has higher charge stats)

This means polearms and spears combination could be more effective than swords and spear combination. I mean using 100 spearmen to pin enemy, especially cavalry, and charging polearms toward enemy flank (since polearms don't care about the cohension of their formation)

The reason I said "especially cavalry" is because I love killing enemy cavalry. They are a big threat with their high attack and charge stats, incuring enormous damage as long as they exist. Also, the general and king, and princes are usually cavalry, and when u destroy them, well, u are about winning the battle.
Not to mention, polearms are number one killing unit against cavalry

I guess I am saying in high and late eras, I am willing to use polearms instead of swords, because the benefits of killing cavalry and other armoured units from polearms' higher charge and A-P bonus, are greater than the benefits of swordsmen's higher attack and moral stats.
(this is of course the attack and moral stats are not too much higher)

I hope this makes sense.

ps: I am playing XL mod, and I think the author has readjusted most of polearms' moral stats, so they are higher in XL than in orignial version.