In my experience Bera is the tougher proposition. Freya as tank invites all sorts of anti minion counters like Skadi, Grimble, Noor, even Gefjon to a lesser extent. There is little harm in dumping tiles into her until you get enough matches to charge up and start taking out the dangerous heroes - in fact Freya’s most dangerous trait is when I accidentally kill her and she cuts my mana. Bera is less pleasant to dump tiles into, firstly for the poision and secondly she will try to shut down your own minion attack. I find I have to be a lot more strategic with how I take her out, and I try to take her out first vs last, despite the mana cut.
My team is Grimble, Noor, Gefjon, Grazul & Lady Loki/G Falcon, so kind of tailored anti minion and anti DOT. I don’t know how much more effective Bera would be than Freya against a less specialised team.