Leafeon would be your best bet because it has better base stats than Flareon. With Leaf Blade, Swords Dance, Baton Pass, and Aerial Ace he can start off by powering up, hit hard and then Baton Pass the attack boost to someone else should he need to switch out. To get that set though, it will have to stay as an Eevee until level 37 to learn Baton Pass.