Assuming that choosing units from normally unplayable factions is allowed, I'd plump for the Numidian Desert Infantry. They are not a particularly strong unit but in my view they are excellent value for money. Their hardiness and bravery also make them a good defensive unit in your home territories, where they can shield Numidia's archers from cavalry attack, and outlast the enemy under the desert sun. But must importantly, they are characterful, plausible and have a cool model.