Choosing your beginner Pokemon is one of the most important decisions you can make in a Pokémon game, and Sword and Protect no exception. If you can't choose which starter, we have noted a number of things for you to consider.
For the first time in Pokemon history, all three remained as their pure typing through their third evolution. Scorbunny will remain the type of fire, Sob will remain the type of water, and Grookey will remain the type of grass.
That being said, they are still all learning various movements of all different types.
Whatever starter you choose, there won't be much difficulty. The first three gym leaders in the focus game type of grass, type of water, and fire type, in that order, which means every starter will have the chance to shine once you start taking down the gym.
In the short term, Grookey will be the best starter to choose, because it will be very effective in the second gym, and will not add damage in the first gym (easier).
Technically Scorbunny also has a slight edge over the others in subsequent matches since the sixth gym leader, Melony, is an ice specialist, but only in Pokémon Shield. In Pokémon Sword, the leader of the sixth gym is Gordie, a stone type userso Sob and Grookey will be more helpful against it. Although at that time you probably already have an alternative Pokémon to help fight them (if not several).
It should be noted that the route before the first sports leader, Milo, is filled with a variety of Pokémon, so it's quite easy to pick up something to level the pitch, even if you start with the Sobble (the weak one on the first) Gym). For example, psychic and flying types of medicine can be found in Galar Mine just before the gym. Types of grass, fire, and water can be found shortly after you start your adventure, so you will never be in a very disadvantaged position.
In short, choosing the "wrong" starter will not dramatically affect the difficulty Pokemon Sword and Shield, so you should only choose which one you like the most. Or which final evolution doesn't horrify you.