Great Attack and Defense and enviable HP make Infantry the kings of close combat. Place them at the forefront in battle.
Even though Cavalry's Attack and Defense are middling, their Speed more than makes up for that. Send them on operations you want done fast.
Their stats are a little weak, but that's balanced by a huge Attack Range. They can hang back to protect themselves while pushing back the enemy with massive damage. So, they battle best from the back of your army.
Don't criticize Priests for their low Defense and HP! They'll win you over with their Massive Attack and Attack Range. Like Archers, they perform well when placed far from the center of battle.
Colossuses can be stationed to defend your Castle Wall from invasions. Recruit more to raise your castle Defense. Your recruitment limit is controlled by your Castle Wall level.