If you're looking to build the best possbile Pokemon Team for the Main Story, there is no doubt that you would need to begin by choosing Scorbunny as your Starter Pokemon. Even though none of the Starter Pokemon can have their awesome Hidden Abilities when chosen at the start of Pokemon Sword & Shield, it is still the best Starter Pokemon one can choose. This is because Cinderace, Scorbunny's FInal Evolution, is a fast, offensive Pokemon with an exclusive power Attack known as Pyro Ball.
A good Partner to Cinderace would be happen to be Gyarados, which can be obtained extremely early in the game since you will have the Fishing Rod at the start of your journey and Magikarp can be found in fishing spots in many of the early routes that contain water. Magikarp will evolve in Gyarados at Level 20, giving you a Water Type Powerhouse before even the first Pokemon Gym.
From there, a Pokemon like Toxtricity will be able to give you additional coverage. It's part Electric Type (which will help deal with Water Types and Flying Types), as well as part Poison Type (which will help with Fairy Types). You can obtain a Toxel for free from the trainer in the Daycare on Route 5, which will evolve into Toxtricity before you'll know it.
To round out this team, the likes of Galarian Rapidash or Hatterene, Galarian Darmanitan and Dragapult will give almost maximum coverage against all types. Galarian Rapidash is preferred over Hatterene since it's much quicker, but since it's only found in Pokemon Shield and thus be traded for in Pokemon Sword, Hatterene will also do since they are the same types. Galarian Darmanitan is a freak of nature, and it will help deal Dragon Type Trainers you'll find later in the Main Story. And Dragapult is one of the fastest Pokemon in all of existence, and it's dual Dragon/Ghost Typing will help take care of Psychic Types and other Ghost Types.
There is little doubt: You can't beat a team comprised of Cinderace, Gyarados, Toxtricity, Galarian Rapidash / Hatterene, Galarian Darmanitan, and Dragapult when it comes to a run through the Main Story of Pokemon Sword & Shield!
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