With the three engine limit, reliability will be key. My guess is that Merc will have the best performance/reliability tradeoff, they’re currently most powerful, so can detune a bit more. I guess that Merc will look at the aerodynamics of Red Bull, Ferrari, and Mclaren and should improve on slower circuits. Renault’s reliability has been poor, so I think they will have to detune a lot next year.
Teams wise, I would say Merc first, Ferrari second, then Red Bull, McLaren, and Renault, but any of those five teams picking up podiums at suitable circuits. Hamilton for drivers’ title, Vettel or Bottas second. Verstappen-Ricciardo and Hulkenberg-Sainz taking points off each other, so Alonso fourth or fifth behind Merc and Ferrari drivers.