My current campaign is with Scotland. I crushed England early on, and France shortly thereafter. Then had a very long off-and-on war with Sicily (who had taken over all of Italy), and finally eliminated Sicily and Spain. Denmark decided to test me, so I've virtually crushed his entire empire now as well. I control all of the British Isles, France, Italy, Germany, Netherlands, Belgium, Austria, Switzerland, and the northern half of Spain/Portugal. Just need about 2 more territories, and to sail an army to Jerusalem to secure the win.

Early on, the highland nobles and highland archers are good enough to take on whatever troops you're facing. Upgrade the armor on the nobles and they tear through enemy troops. Most of my infantry now are noble swordsmen, and I have Templar knights in Angers for cavalry (as well as feudal knights in my other fortresses). Noble highland archers still serve me fine, though I rely on archers less now since I have culverins and mortars with most of my armies.