I'm actually a big fan of polearms over sword infantry, mainly because they're more well-rounded. Sword infantry often has slightly better melee stats, but has one glaring weakness: cavalry, which you tend to encounter a lot of. Polearms, on the other hand, have no serious weaknesses.

Polearms may have lower morale, but this only matters if they get flanked or otherwise in a very tight spot - but this rarely happens with my armies, so the point is usually moot. And BTW, even vanilla halberdiers will chew up almost all swordsmen in a head-on fight, including CMAA and Byzantine infantry. Polearms don't actually have a weaker attack against lightly armoured troops - they just get less of a bonus, while their own armour-piercing weapon helps them deal with swordsmen, spearmen, and cavalry effectively.

Don't get me wrong here - I like swordsmen as well, and make sure to keep some of them in my armies. The real question for me is this: why spears? I know their theoretical use - pinning the enemy, especially cavalry, while something else flanks. But how well does this work in practice? Spears are good against cavalry, as long as they keep formation and don't get flanked, but if they encounter swordsmen or polearms, they fold quickly. They even have problems against some weaker units, like militia sergeants. What's more, I've seen them lose formation even in head-on fights, and once this happens, they die very quickly. Besides, how likely is it really that you'll be able to catch enemy cavalry with your slow-moving spearmen, when the enemy will more likely use his cavalry to target more vulnerable units, like swordsmen and archers? You can more easily meet cavalry head-on with polearm troops - you may lose a few more men to the charge, but you'll destroy the cavalry more quickly and still win quite easily.

I like polearms, swordsmen, and axemen, but spearmen have fallen out of favor with me. Anything with as many weaknesses as spearmen is not worth the investment.