Little shocked to see nobody mention the Danes.

Simply put, Obudshaers are the meanest infantry unit in Europe.

The Viking (Norse) Archers are also extremely rowdy. They remind me of Samurai Archers in STW, not only are they competent archers but they are very solid in hand to hand.

If you anchor your main battle line with Obudshaers and then protect your flanks with some of the other Danish infantry, well, short of HJI you are going to smash everything in front of you to tiny little bits.

With the very solid melee stats of those Archers, you can actually field shooter armies.

In terms of the Campaign, the Danes have more room to expand than the English and are nearly as isolated. Expansion into the Baltic and Finland will achieve you a rich trading network. Then you can slam into the HRE from the north while they are otherwise occupied.

Obviously there really is no way to state what the single most powerful faction is, however the Danes have some exceptionally powerful units with the ability to grow economically without much chance to come into conflict with a rival power until they are ready.