Best attack army

Selucid
3 untis of elephants, (armoured if you can)
3 units of kataphracts
3 untis of companion cavalry
Rest being Silvershield Legion and archers, maybe some Scythed Chariots.

Tacitc

Use elephants to rush the enemy staright on, and rush to the back of the enemy army.
Then the same with Katas and Companion.... well if there is anything left, use the Legions to clean the place.