The polearms tend to do more damage with longer range, and have more weapons that do pierce and blunt damage, which means you don't as much powerstrike as you do with the mostly cut weapon 2hers. Balanced and agility builds work really well with polearms because of the range you often can hit without threat of getting hit back and because of the long weapons you also don't want to get into facehug scenarios with 1hers and short 2hers so having more athletics than a 2her build is useful for your footwork. You can still always do well with a strength polearm build, but more than many classes balanced/agility builds work out well.
Alright, thanks, I'll try one of those balanced builds and see how it goes.
P.S. Which polearm works the best with that build? Poleaxe? Long axe? Or can I use any of them?