Polearms - STUN, cheaper, faster, better range, some of the best price/range/speed/damage combinations in-game (long hafted blade, long hafted knobbed mace), very efficient with low WPF, high versatility (you can be spammer, crusher,shieldbreaker, spearman, cav if you add riding, spearman+shield), better for fighting multiple opponents
2H - better for duels, faster stab, more expensive.
I used to be PA pre-patch and unfortunately switched to 2H post-patch, if I am given the opportunity to trade my heirloomed 2H I will go back to polearms, they seem stronger atm.