I'd like either Ninetales or Muk (even not shiny if it was for me), but if it has to be Silvally I opt for a Fire setup, since it seems more efficient for vgc to me (I'm definitely not an expert, this is purely an opinion xD)
Yeah i use the fire set to counter my weeknesses in battle tree hahah. Its my backup sweeper. Honestly muk or ninetails are probably the most usefull of the four though.