I say Flygon. It's overall better than Altaria.
It's gen 3 so a lot of mechanics and moves are not as you may know from X & Y or ORAS .
This moveset :
Fly - Because you requested it.
Earthquake from tm or you may keep dig
Crunch because that psychic gym
Dragon breath against drake in Elite 4
BTW the best hmslave for that gen is Tropius. He can learn every non water hm.