The Hellen in me screams that I should say Barbaroi are Barbaroi. Filthy, smelly, uncivilised. The worse of the worse. But on a serious note, I don't really think the Suebi are underpowered. They are just (and I guess historically were) more "primitive" than the rest of the factions, meaning they have a more "primitive" (almost naked?) style of combat. Plus, from what I've learned playing the Sweboz for a while, they didn't have easy access to materials like iron, preferring spears and clubs for their heavier dependance of wood (which was rather plentiful that time, they didn't wipe their arses with consentrated tree substance that time).
As for which "barbarian" faction I believe is the best, or better the coolest, I would have to vote for the Lusotannan. They have cool units, and have great potential. Their excellent armour and guerilla tactics, as well as a possibility of more Roman-like "manipular" formations, make their armies quite impressive on the battlefield.
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