Pokemon Sword and Shield's Grass-type Starter Pokemon sticks to a drumming theme. As with other Pokemon games, Pokemon Sword and Shield offers players a choice between three Starter Pokemon at the beginning of the game. The Champion of the Galar region, Leon, lets players decide between either Grookey, Scorbunny, or Sobble. A player's Starter Pokemon becomes a core part of their team, especially during the player's early journey, and it will likely be one of the first Pokemon that they evolve.
Grookey, the mischievous chimp-like Grass-type Pokemon, seems to enjoy drumming as evidenced by the stick it always carries with it. Grookey uses the stick to tap a beat on anything it encounters, and that characteristic sticks with it even after it evolves. Grookey eventually evolves into Thwackey - a pure Grass-type Pokemon. Thwackey carries two sticks that it uses to hold back its leaf-type hair when its not in battle. Thwackey evolves into Rillaboom, another Grass-type Pokemon that resembles a gorilla with a long mane of leaf-like hair, at Level 35. Rillaboom carries a large tree stump with it at all times. The roots of the stump are said to follow its directions in battle, which is why it learns the special Grass-type move Drum Beating when it evolves. Rillaboom's Drum Beating attack deals damage and lowers a target's Speed stat, making it a potent attack in battles.
Here are images of Thwackey and Rillaboom below:
There's no real advantage to taking one Pokemon over the others - the first three Gyms are Grass, Water, and Fire gyms, so players will have an advantage at one gym, a disadvantage at another, and will face a gym leader with the same type of Pokemon in the third. So, basically your choice comes down to what Starter Pokemon you like and what Pokemon you feel would make a good foundation for your team.