Dedenne and Greninja - The game is full of double battles, and I lead every single double battle with Dedenne and Greninja. Greninja mat blocks while Dedenne discharges before switching to Thunder/Play Rough/Grass Knot. Greninja can sport Spikes as well for double battles which might be a bit controversial but allows damage to be made by Double Battle Pokémon and makes it immune to Discharging Dedenne.
Medicham - Pure Power + Hi Jump Kick is incredibly strong and also makes training with the audino trainers easy