Plusle or Minun. The only issue is training them up to level 19 so they can learn spark. You can then round out its moveset with solid moves like thunder wave, charm, encore or thunder. They're both pretty fast and you can get the magnet from the trick house and give them the thunderbolt tm from new mauville if you want. With all the water and flying types in the game they'll see plenty of battles and come out on top way more times than not.
