Water: Vaporeon. He's amazing.
Grass: Venusaur. I originally picked him and fell in love with him.
Fire: This one is hard. I'm gonna say Ninetales, because I never see him being used and I personally love Ninetales.
Fighting: Scrafty because he's so useful in the Elite Four of Unova and without him I would have lost in the Elite Four.
Dark: Scrafty, like I listed above
Psychic: Alakazam because he's a beast.
Ghost: Gengar because he was on my original FireRed team and I've never really used any other Ghost types.
Steel: Lucario because he is awesome.
Bug: Kricketune, he has a moustache.
Poison: Toxicroak, he's a frog.
Dragon: Dragonite, he's amazing.
Flying: Also Dragonite.
Ground: Quagsire, I recently used him in my run of Pokemon Gold and he was amazing.
Rock: Golem because walking rock.
Normal: Snorlax because he is useful in every game I've used him in.
Electric: Luxray because I love cats and he is useful in Platinum and HeartGold.
Ice: Mamoswine. I like his tusks.