Brittannia. Chariots.
Germania
Britannia
Brittannia. Chariots.
Really depends what you are facing. Campaign on vh/vh I find Britain's mass chosen swordsmen and chariots particularly irritating to combat on open fields, as Julii.
Online? Head hurlers are only scary if you let them be. Chariots are far harder to counter, but I'd say Germania takes it as easiest to cause a mass route with access to night raiders, wardogs, heavy cav, ect.