Ok, so by now, the enemy, and yourselves, have gotten better troops, and the battles are becoming quicker some times and harder the other times. You are probably at war with at least One Catholic Faction by now, so this is when you need to get some Crossbows in your army. You can get Mercenary Crossbowmen at the start, and these are a prime example, in attack power at least, is of what is to come in later times. These guys are the unstoppable force in the early game, but will soon be taking a backseat as the professionals get to work.
So, if possible, get some Crossbowmen into the fray! Kick some peasant archer ass! Win a few battles and you will definetly change your mind if you think crossbows suck ass. I was able to hold off 2,700 Milanese soldiers with 1,000 French Mailed Knights, Armoured Sergeants and Mecenary Crossbowmen. The enemy lost 50% of it's army before it even made it to my lines. I flank charged and the enemy was routing faster than you can say, "Holy Robin Hood

in a castle moat!"
But, that's if you are a European faction or the Moors. In the Middle East, it's archers. And it'll be tough to hold off Mongol and Timurid incursions into your lands with Horse archers. Now, don't get me wrong, Horse archers can be better than foot archers(and, in many cases, are), but the Mongolians will make

hit the fan. Once you even make contact with their Melee units, the unit you sent to attack will be on Shaken, Steady, if you're lucky, Morale. The Mongols can rout a full stack of yours with Six of their units. Trust me, I've experienced it first hand. The Timurids are worse. Why, you may ask? Well, let's see. What's Big, Grey, has large ears, a long nose, makes a frightening noise and has a Cannon on it's back? That's right.
Michael Jackson Elephants. 'Nuff said.