Reasoning:
Grass: I just like Bulbasaur and honestly is my favorite Grass starter
Fire: I love Vulpix....
Water: I was going to choose Squirtle since its my favorite Water starter but Lapras won me over back during Orange Islands Arc. Also is a fitting Surf/Rider Pokemon.
Normal Type: Eevee is well... awesome.
Electric: Can anyone really beat Pikachu?
Psychic: Meowstic kind of won me over in X/Y.
Fighting: Hariyama is the definition of FIghting types in my book.
Rock: Kabutops was a bad-ass Rock Type from Generation 1 that gets lost in subsequent generations.
Ground: Being a pure ground type, Sandshrew is to this day my favorite. Underrated Pokemon too.
Flying: Pidgeot is one of the best Flying Types and I'm still waiting on Ash to visit his.
Bug: Butterfree was the first Bug Type I came to love and like with Pidgeot... waiting on it to return.
Poison: Not fond of Poison Types but Nidoqueen is one of my favorites.
Dark: Umbreon hands down. Design is sick and it can fight too.
Ghost: Gengar is what started it all and I haven't found another one to be better.
Ice: Did I mention I love Vulpix? Yeah... enough said.
Steel: Like with Poison, Steel types don't appeal to me but Steelix isn't that bad.
Dragon: One Like, One Hug for Turtonator
Fairy: Sylveon is hands down my favorite. Still salty that Ash hasn't caught a Fairy Type yet, much less an Eevee.