Probably a flying gym. Sure, I'd get steamrolled by an electric trainer, but having an flying-themed gym sounds really cool, and there are plenty of decent Flying pokemon out there.
It's ok to choose Tyranitar. After all, almost EVERY dragon-type leader/champion has a Gyrados, even though it's not a dragon type. (Thank you, Gen 5!)Dragon type of course! My team would be Haxorous, Salamance, Garchomp, Hydreigon, Tyranitar(I know not dragon), and my main pokemon, my fav, and the best of my team... Draginite!