Choosing your starting Pokémon is one of the most important decisions you can make in a Pokémon game, and Sword and Shield are no exception. If you've got stuck on which starter to choose, we've noticed a few things to keep in mind.
For the first time in Pokémon history, all three starters remain as their pure typing through their third evolution. Scorbunny will remain a fire type, Sobble will remain a water type, and Grookey will remain a grass type.
That said, they are still learning all the different traits from all different types.
Whatever starter you choose, there will not be much difference in difficulty. The first three gym leaders in the game focus on grass types water types and fire types in that order, which means that each starter will have a chance to shine when you start taking down the gym.
In the short term, Grookey will be the best starter to choose, as it will be super-efficient in the second gym and will not add further damage to the (lighter) first gym.
Technically Scorbunny also has a slight advantage over the others in the latter game because the sixth gym leader, Melony, is an ice type specialist, but only in Pokémon Shield . In Pokémon Sword, the sixth gym leader is Gordie, a clipper user so Sobble and Grookey would be more useful to him. Although you probably already have an alternative Pokémon to help them (if not more).
It should be noted that the routes before the first gym leader, Milo, are filled with a variety of Pokémon, which makes it fairly easy to take something to level the field, even if you started with Sobble (which is weak in that first gym). For example, mental and flying Woobat can be found in the Galar mine just before the gym. Other grass, fire and water types can be found shortly after you start your adventure, so you will never have an extreme disadvantage.
Long story short, choosing the "wrong" starter will not dramatically affect the difficulty of Pokémon Sword and Shield so you should really only choose the one you like best. Or what final development doesn't scare you.