I usually have several stacks around, so that I can pick and choose the makeup of my army based on that of the enemy. I generally don't have more than 3 units of archers on the field at a time, 2 units of spears spread out 3 1/2 ranks deep, 6 or 7 men at arms and billmen combined (depending on the enemy) and the rest cavalry. I've really fallen for the English billmen trained in Mercia for the valor upgrade and retrained in an iron province with the max weapon and armor upgrade available at the time. Those guys absolutely slaughter any cavalry that gets near them, especially if I am using one of my 8 or 9 star generals. They are so effective that I end up using my cavallry as an anvil to keep the enemy cavalry from running away so that my billmen can act as the hammer and rack up some kills.

I only use crossbows and arbs when I'm fighting those massive stacks of horse archers that the horde sends my way. pavs are the only way to make any headway against them since they are so fast and never sit still to take a beating. I guess I would also use pavs against the big stacks of jinettes except that I always knock out the Spanish before pavs are available because I want all those Iron provinces and because I can defend all that land on the penninsula with just one army in Cordoba.