I voted Rayp, Boreas, Nosferatu.
All three are good, solid decks with weaknesses you can take advantage of using existing god killing decks.
A majority of the others would be so overpowered with the extra draw and marks I don't even want to think about playing against them, you should beat new gods with the existing decks at least 50-60% of the time, not even more auto-losses, we have enough of those already.
Gods that can only be beaten by a specific strategy are not good, as you don't know which one you'll fight against, and obviously that specific deck will be weak/useless against the others.
Any new god that kills a fractal/ray god killer deck are not good because that's the ONLY non-rainbow god killer at the moment with a good win rate, and everyone is already sick of playing rainbow all the time.
(And I don't see new god killer decks to surface any time soon unless they get nerfed)
On a side note...if gods would get nerfed, most of these decks would be awesome...but with the current advantage for gods, they'd be near unbeatable instead.