It depends on the game stage.
Early game light cav or horse archers. Lightly armored enemies, unshielded infantry stand no chance even if they out number you greatly so they are great as long as you are fast on the map and pick your battles
Later I will mix this with heavy cav, horse archers can harrass the enemy while the heavy cav mow down opposing organized cav or archers
Much later I often do a hard transition to heavy infantry
BTW I think your poll left off horse archers