I think NG is clearly the strongest in this seasonal mode. It has a lot of killing machines, high provision, low body, that can brick in regular mode but here are always a safe bet. On top of Igni and Geralt that is seen in every deck, you have Leo who's another auto-kill, Shilard who has never been that useful and assire to replay roach... All on deploy. The other factions have either some big units that don't beneficiate as much from the seasonal mode, and all engines that you boost will get destroyed.
I've ran an Eithne deck with scorch, igni, schiru and other scorches which was pretty fun. But if you try to build something, to set up something, in this mode, you'll probably get countered. You can still try different techniques though. I've been grinding on my Usurper mastery (since I don't really like the leader in ranked) and made a little different deck just focused on messing with the oponent's deck. Infiltrators, graveyard messing around, Cynthia, Assire to put back fillers, Shilard (if you get to keep Syanna alive, it gets really funny), etc...
What really surprises me is that we don't see that many Foltest decks which could potentially run more removals than NG with its zeal... Oh well, I know what I'm doing next XD