I think of troop combinations as a graph with many peaks and I use many peaks.

I first thought that using spearmen and cavalry was the best tactic and it still is for many situations. You can hold anything in position with spearmen, for a while, then flank them with cavalry.

I then became a cavalry addict, I'd usually bring infantry into a battle along with me, but get impatient and just swarm the enemy with cavalry, charging through cracks in their line and flanking everything and anything, even halberdiers. This also works and I occasionally use this tactic.

I then started to use an archer spearmen swordsman arrangement after I realised that decreasing casualties is the key to victory (to have a full army after the battle is wearing on means victory, have you ever wanted just one more unit of men at arms standing by, to help your 20 knights kill off the remaining 40 halbs?) and noticed that spearmen are practically only used for stopping cavalry and pretty much a waste of space, so I developped a stereotypical, archer infantry cavalry troop selection.

I then went back to using spearmen and cavalry, except to use the spearmen to draw troops of a hill and flank them william the conquerror style, except with the cavalry and infantry roles swapped.

I never really use 1 unit, they all have their strengths and weaknesses and I have to use more than 1. Though I guess cavalry are extremely useful in attack and men at arms in a forest are extremely good in defense.