They are best used where the decisive action will take place, either to force their way through enemy infantry, or to repulse the heavy cavalry of the other Greek states.
Hail Stratege! Your finest warriors, the true elite of the polis, stand here before you. They are drawn from the bravest and wealthiest men. They eschew the horse, preferring to allow their brothers who are too cowardly to fight on foot the role of cavalry. They are armored in the finest bronze armor, with shields made from only the best and stoutest wood. These shields are faced with fine leather or bronze, and in the skilled hands of your greatest soldiers, they can stop all but the most determined blows. The spears of these fine soldiers are made from the best cornel wood and iron. All of them are battle tested veterans. None will shirk from the shield wall and the killing, for each regards it with the cold dispassion of an elite soldier that belies their name: the Epilektoi, or picked ones.
Historically, the Greek poleis fielded small numbers of extremely hardened and well armed warriors. These soldiers were every bit the match of the elite units of other nations, as proven in engagement after engagement. They are best used where the decisive action will take place, either to force their way through enemy infantry, or to repulse the heavy cavalry of the other Greek states.
If the humble Hoplitai (Greek Classical Hoplites) were a formidable and unbreakable wall of shield and spears then these men an unstoppable force.
These men may be used to defend the most dangerous parts of the battle line or as a reserve unit acting as a infantry version of a heavy cavalry unit with their powerful charge and attack. They can also be used to destroy enemy cavalry or generals after trapping them.
Their armor and shields can shrug off most missile from the front and also makes them very difficult to defeat, having them in guard mode will make them hold on as long as you want.
Beware of anti-armor units like axemen or falxmen, especially if they are attacking from the flanks or the rear.