Source images: Game Freak, The Pokémon Company/Nintendo
Pick a random starter to make your next playthrough more challenging. Simply click generate and you'll get a random starter Pokemon from generations 1 through 9.
Along with this, you'll be presented with a randomized moveset and the Pokemon's hidden and standard abilities.
If we are including Mega Evolutions, the best starter is probably Charizard. The Kanto starter has access to two forms, X and Y with great abilities, stats, and typing.
However, my personal favorite starter is Totodile. While not as competitively viable as Charizard and Greninja, it has a few traits that make it a decent addition to your squad.