I had say that you should use Garchomp (Flygon is statistically worse), as it is extremely useful to defeat Ghetsis and N. They are your main threat. Although Krookodile can learn Dragon Claw, it can't outspeed his Hydreigon and Zekrom. Type overlap doesn't matter here, as only Vanilluxe threatens them (you have Emboar to defeat that, right?). Your Steel typing has already overlapped, so it doesn't matter.
Or you could choose Haxorus. It can even take care of his Seismitoad using Grass Knot (approximately 60 SpA stat + 4x weakness = 120 SpA stat + 2x weakness).
Garchomp @ anything.
Ability: Sand Veil
- Dragon Claw / Dragon Rush
- Dig / Earthquake
- Crunch
- Rock Slide / Stone Edge
Haxorus @ anything
Ability: Rivalry / Mold Breaker (latter is preferred, it can demolish Eelectross)
- Dragon Claw
- Swords Dance / X-Scissor
- Earthquake
- Grass Knot
Hope this helps :)