Honestly, we're still way too early to make strong decisions about faction balance. This is not an easy game to optimize and level of play is very low, so there's a long way to go.
I guess first impressions are useful, though? The Barbarians seem like they're the weakest, but only in terms of their being a little bit more affected by luck than other factions - they're still strong and effective, if tricky to play.
I was going to post this exact thing.