Pikachu, definitely. I'm getting a Pikachu, if only for the simple nostalgia it brings. Watching the anime and rooting for Pikachu, or walking around and battling with your own Pikachu in Pokemon Yellow. I just can't pass it up now that its in the game. He'll take the starring role of the Main Character in my team.
Lucario, as the main offense. If I remember correctly, it had an particularly good offense being a fighter, but its defense needed some work, at least for the particular Lucario that I caught. It'll be in the second slot, as a supporting character for Pikachu. Whenever I encounter a normal or a tough enemy, Lucario takes the lead!
Fennekin, starters are a necessity and Chespin and Froakie just didn't appeal to me. A fire fox, thats been done before by Ninetales, but I decided I should give it a try. After all, a fire fox sounds fun!
Sylveon- I really think this is a Fancy Pokemon. Bows are really classy. Jokes aside, if I remember correctly from the rumors, its good against Dark, Dragon, and Ghost. Dragon fights can be really messy, so I'll just throw out Sylveon whenever I encounter a Dragon and let it faint the Pokemon in style.
The other slots will be reserved for any interesting pokemon I decide to catch while I'm out exploring the new region. Well, thats my team! I know it could be a lot better as far as balance and stats go, but I'd rather have this bunch of pokemon. And I don't think I'll have to change it up, it shouldn't be too adverse.