My favorite stack depends on what I have. The Byzantines have some good units that are very hard to reach. So Mostly I have to use what I can get.

A normal early army looks something like this.

Spear Militia X 6 Used as a shield wall
Byzantine Spearmen work but don't get the free upkeep in a city

Archers X 6 Trebizond Archers are my favorite

Infantry X 4 Byzantine Infantry/Spearmen/Mercenaries/ Spear militia
I don't have much to choose from here.

Cavalry X 3 HA's

General X 1

If I really need to win the battle I'll put 4 family members as the cavalry because those are the only heavy cavalry the Byzantines can reach for a long time.