I put Gorgotha / Mab / Valk / Mab ahead of the Soothsayer version. With a caution that you never use either version of that team against lineups with impervious or mana shield (though Gorgotha gives you a little insurance if you don’t scout or don’t realize what traits your opponent has).
In terms of play, I focus on filling up either Gorgotha or Valkyrie first (whichever has a better opening board), then using Valk to fill Mab and generate blue. The ideal situation you are aiming for is to have both Mabs charged and have 13 blue on the board (either lucky drops from a Gorgotha cast or by carefully using Valk to generate the additional blue that you need). From there, you can cast Mab, get a free turn, cast Mab again and, in a perfect world, cast Valk to refill one or both Mabs and collect another free turn to cast Mab another time or two. Whenever things grind to a halt, cast Gorgotha to reset the board and refill the other troops.
Each time you cast any of your spells, both Mabs are gaining +1 magic due to her Arcane trait and each time you make a match 4 or 5, both Mabs are randomly freezing an enemy troop. With Valk and Gorgotha generating a lot of Match 4’s and 5’s, and Mab and Valk cycling extra turns, you get a lot of bonus magic and freezing.
As long as your opponent has no mana shield or impervious troops, this team is unstoppable once you can power up Gorgotha.