Just post your favorite unit and the faction in these categories; Heavy infantry, pikemen, light infantry, light cavalry, heavy cavalry, skirmishers, bowmen, cavalry archers, heavy cavalry archers, siege, strange unit (war dogs, incendiary pigs, screeching women and the like.)

Heavy Infantry: Praetorian Cohort (they're just cool)
Pikemen: Poeni Infantry (my main stay infantry)
Light Infantry: Scutarii (are awesome with some experience and weaopn upgrades)
Light Cav: Long Shield Cavalry (actually a medium cav unit, but cheap and reliable. Also carry a punch when needed.)
Heavy Cavalry: Sacred Band Cavalry (battle winners IMO)
Skirmishers: Cilician Pirates (best skirmishers in the game)
Bowmen: Balearic Slingers (are almost more devastating than archers, especially at close range.)
Cavalry Archers: Numidian Cavalry (pretty much a unit capable of doing lots of stuff. Very versatile and has good speed too.)