There was a locked thread for this, and I posted my faves there. I'm not gonna use double types to fill my faves though. I'll have a new Pokemon in those types.
Normal: Granbull - He just looks like a tough guy ahaha. I like him for that!
Fire: Houndoom - He's a doberman, and breathes fire and pulsates dark energy. What is there not to like?
Water: Omastar - Destroyed in Blue for me. Hydro Pump, Surf, Blizzard and Horn Drill is a hilarious moveset, especially for a guy like me who gets lucky with bad accuracy moves. I use Omastar regularly to this day!
Grass: Venusaur - He's just sick. A quadriped dinosaur with a huge blooming flower on his back. What's not to like?
Electric: Galvantula - Can learn to spiderweb attacks, can potentially have 91 base accuracy for Thunder, and Galvanize may be one of the best words in the English language.
Bug: Pinsir - There are so many bugs I love, also Masquerain, Shedinja, Ninjask, and Galvantula, obviously. But Pinsir was around first and he's a monster. Venomoth too but he's going in Poison.
Poison: Venomoth - He looks really cool, and has probably my favourite voice in the show, aside from Breloom.
Fighting: Breloom. He's looks SICK! It's a shame how people only use him for Spore and Focus Punch, though. 130 base attack and the best voice in the show. Can't go wrong with this guy.
Flying: Crobat - Ran faaaaast through Ruby with this guy leading my team. Torched the Elite Four as well, someone survived against Glacia. (I'm lucky with Attract).
Rock: Probopass - Although if I could get rid of his mustache I certainly would!
Ground: Marowak - Bonemerang is the best name for an attack. Looks really cool too.
Steel: Bisharp - Based off of the bishop chess pieces, and he's also part dark. <3
Ice: Froslass (looooooooooooooooooooooooove Snorunt) and she makes him really cool.
Psychic: Espeon - favourite with Umbreon.
Ghost: Whatever the ghost evolution that Eevee eventually gets is. Ahaha.
Dark: Umbreon - favourite with Espeon.
Dragon: Kyurem Cool backstory