That's weird--I would have guessed your favorite was Banette! Oh well, just kidding.
Some of my favorites are:
Ninetales: (Well, duh, it's my username!) Because it can have so many different abilities in its tails... It's a very mysterious Pokemon, almost like a legendary Pokemon. Plus, its personality matches mine--it's smart, vengeful, and won't hesitate to put curses on people when necessary!
Gardevoir: It was my best Pokemon in Sapphire. I really liked Ralts from the moment I found out it was Psychic-type, and when I discovered Kirkia and Gardevoir on some website, it was love at first sight! The Pokedex entries for them appealed to me, but I think Gardevoir looks cooler.
Alakazam: Who wouldn't like the smartest Pokemon there is? Well, anyways, Alakazam was a favorite in the games as well. I would have put Kadabra on my favorites list because of its first appearance in the anime (lol--Sabrina's my favorite trainer!), but... I like Alakazam better?
Misdreavus: It's gotta be the cutest ghost Pokemon ever! I like its personality (its mischievousness), and, again, it was love at first sight! (Or maybe I like it because I created a really neat evolution for it!)
Hypno: I liked Hypno ever since it appeared in the Pokemon episode "Hypno's Naptime", for some reason. But, in Yellow, when I couldn't beat the Elite 4, I raised my Hypno from level 34 to 60, and it actualy helped me beat the Elite 4! So maybe that's the reason... Or, maybe it's because I made a cool evolution for it!
Dragonair: The only favorite that's not fully evolved. I like Dragonair because of the way it looks, as well as its mysterious aura and ability to change the weather. I usually am drawn away from brawny Pokemon like Dragonite.
Banette: The only favorite that won't appear in the Pokemon game I'm planning to make... Banette reminds me of myself--it's sadistic, vengeful, dark, and likes to put curses on people. (Well, sort of...) Or maybe it's because it plays an important part in my Pokemon fanfic...
Darn, I named seven; that's my unlucky number! Heh, oh well, that's just naming a few...