I have kinda of a bad memory for the first generation because the first time I played the game it was a friend game and I'm not sure if he had Blastoise or Charizard so.
Gen 1- I believe it was Charmander but migth have been Squirtle
Gen 2- Cyndaquill(Gold)
Gen 3- Treecko(Ruby)
Gen 4- Chimchar
Gen 5- Oshawott(because of Dewott), was going to go with Snivy, then saw Dewott and all the Oshawott memes and went with Oshawott, then saw Emboar and wanted to go Tepig but went Oshawott either way
Gen 6- Rigth now going wit Froakie and I don't want to spoil myself besides CoroCoro, so I maybe chance opinion with the middle stage starters since they migth be revealed