What is my favorite starter trio? That is a really good question, Megan. I haven't given it too much thought until now. Normally, I just enjoy individual starters such as Feraligatr, Blaziken, and Serperior, but as a whole trio, answering this question might be interesting! I really enjoy the starters from the Galar region. I love Inteleon and its ability to improve your play-through by being able to land several critical hits and inflict extra damage with its Sniper ability, which is especially effective when combined with the friendship feature. I also love Inteleon's ability to be a great special sweeper competitively as well, especially in the Rain. I love Cinderace and its Libero/Protean ability, which allows it to change types based on the move it uses. It ensures that Cinderace always hits with STAB and is very powerful. I love Rillaboom and its ability to do some serious damage as a wallbreaker. I love its ability, Grassy Surge, which boosts the power of Grass-type moves among other things and gives Rillaboom priority when using Grassy Glide, a move that becomes extremely powerful as well in Grassy Terrain. The Kanto starters are also great. I love Blastoise for being able to use Shell Smash effectively, making it a deadly sweeper, especially after Gigantamaxing. I love Charizard for being so great after Gigantamaxing as well and being really good to use in Doubles. I love Venasaur for being perhaps the greatest special sweeper in the Sun. If I had to choose between the two as a whole, I might have to go with Galar. You can't go wrong using all of those!
Individual favorites per type: Blaziken, Feraligatr, and Serperior. Blaziken is simply amazing. It has Speed Boost as an ability, which is broken and allows Blaziken to be a feared sweeper. I love Feraligatr's design. It reminds me of godzilla in a way. Its ability, Sheer Force, allows it to hit like a truck when holding a Life Orb and can sweep teams after using Dragon Dance. Serperior is great for simply being the underdog, or undersnake in this case. She has a great design, a smug snake, and with Contrary, she gets Special Attack boosts with Leaf Storm instead of reduction! I love it!