If I were developing a new Pokémon game, I'd want to choose starters that are both unique and appealing, with interesting type combinations that haven't been done before. Here are my choices:
Fermos: A Fire/Fairy-type Pokémon that resembles a small, fluffy fox with embers in its fur. Fermos would be a Special Attack-focused Pokémon with high Speed, designed to be a fast and powerful special sweeper. It would have abilities like Blaze and a new hidden ability that boosts Fairy-type moves in harsh sunlight.
Krakle: An Electric/Ground-type Pokémon based on a small, mudskipper-like creature. Krakle would be a Physical Attack-focused Pokémon with high HP and Attack, built to be a bulky attacker. It would have abilities like Static and a new hidden ability that grants immunity to Water-type moves while boosting the power of Ground-type moves.
Leafen: A Grass/Poison-type Pokémon that looks like a leafy sea dragon. Leafen would be a mixed attacker, with balanced Attack and Special Attack stats, as well as decent Speed. It would have abilities like Overgrow and a new hidden ability that heals it slightly each turn when poisoned.
These three starters would offer a good balance of offense and defense, with unique type combinations that would make for interesting gameplay.