England
I agree with Yakobu. In the first two turns of Early, abandon Aquitaine and Anjou, moving thier forces to Normandy. At the same time, move the archers from Northumbria and Mercia to Wessex. On the third turn, invade Flanders from Wessex and Normandy. The French will retreat, you have only one front-line province to defend, you have THE richest province in Europe (I'm pretty sure) and you are free to take Wales, Scotland, and Ireland at your leasure.
Also like Yaboku said, you can eventually invade Scandinavia, take out the Danes, and push as far as Saxony all the while only having two front-line provinces (including Flanders). In early you get Hobilars (light cav), a discount on the cost of Archers, Fyrdmen (upgraded spearmen), Highland Clansmen, Gallowglasses, Kerns, and Irish Infantry. In High you get Longbows (who are badass) and Billmen who are cool too.
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