Mmmmm...it seems like the sad reality is, that there is no best unit in the game. if there was, then everyone will be exploiting them, and it will pretty much be used everywhere, and no one else would want to use anything else. the game, and all strategy games are created such that ALL UNITS will have strengths, but WILL have weaknesses. spartans, cohorts, chosens, bowmen and elephants have been thrown around this forum, hailed to be the best unit, however, someone is still able to successfully identify its flaws-from flanking, archery, speed, mobility, flexibility, and cost. It just goes to show that no unit is the best, or perfect. it is the combination of certain units that makes an ARMY, close to invincibility and immortality much much closer than just a single unit.

HOWEVER, i place my bet on ARMOURED ELEPHANTS to close to the 'best' unit the game, since NO UNIT (apart from from the pigs) are capable of defeating it singlehandedly without being crushed under elephant feet itself.