Here's a Viking campaign answer: archers and Viking landsmenn. Maybe a raider cav for mopping up routers, but that's optional. Whatever's coming, shoot it up then chew it apart. Never seems to fail.

Is it just me or are the Viking units pretty darn invincible? Churning out landsmenn and even huscarles is really easy and they just chew through pretty much everything. Landsmenn will even take down horsemen without taking many casualties.