If we started a poll about best defensive unit, I would choose the Byzantine Infantry. They are solid, elite, difficult to route, good attack and defence plus chape. With the help from missiles, not even French Knights or Mongol Cavalry can charge them.

Exile, it seems that the AI Islamic armies emphaized on cavalry, that means too much mobility but not enough stability. Such forces are strong in assault, but they are useless if the opposition possess solid infantry. The terrain in Asia Minor is highly defensive. My favourite tactics as Byz is to use the Byz infantry to absorb the shock from charges and laid down an supporting barrage by the archers. When the enemy become tired, the heavy cavalry would be unleashed and even a head-on charge would succeed. The timing has to correct, otherwise my own troop would become tired and wavered.

By the way, desdichado, what's the composition of the enemy's force? Mainly cavalry or else?