A Magneton I guess. It's electric and steel types are easily defende by the rest of your team. Just make sure that they know some supporting moves to cover each others weaknesses.
Water Pokemons are very useful. They not only can take you across the ocean, as well as are in advantage to the most offensive Pokemons, which are fire and ground types. Teach an ice move to your water Pokemon and it'll be also cover your weaknesses to dragon, flying and grass foes.
Seriously, whatever floats your boat, every pokemon has an expanded movepool in Omega from Charizard with Dragon Claw to Alakazam with leaf blade and luster purge.
Hunt around or download the YAPE (Yet another pokemon editor) to see what they've got.