Horse archers (even vanilla HA) In the beginning of the game I even conquer provinces with only HA (or Turcoman Horse or Szekely) Excellent against rebel troops that don't have archers (or only 1 unit that you run down instantly) I take 1 or 2 spearmen and maybe one other foot troops.

Later I add some heavier cavalry, foot archers and slowly every type as needed. However I am not such a big fan of heavy infantry troops. I like flexibility and they are slow and tire fast. They just don't fit my style: I usually win the battle with the fast units by the time the slow ones catch up (it is good the catch the enemy moving before it dug in on a hillytop with its back to the edge of the map.)