Flying for Flying because Hydreigon has good moves that come in handy when battling the Elite 4. Just a reminder that Zweilous evolves at level 64 so be wary of that.
As for Flying types, these are the recommended ones:
If your starter was Tepig
Swanna is a very awesome bird that can really be useful in-game especially if your starter was Tepig then you have a flyer and a surfer. Not to forget that Swanna has acces to Brave Bird
Swoobat is a decent flyer too and is incredibly fast. It's downfalls are it's poor defences but it is truly a nice edition
If your starter was Oshawott
If you chose Oshawott then I recommend Unfezant. It is a very decent Pokémon with pleasing a attack statand decent speed. It has a very shallow movepool though. But this is a nice moveset:
Unfezant @ Silk Scarf
Nature: Jolly/ Adamant
Trait: Super Luck
Swoobat is also an option
If you starter was Snivy
If you chose Snivy then I recommend Swann. Swanna is a truly fantastic Pokémon to have and a great aid to many teams that lack a surfer
Swoobat is always the second option as it has great speed
But there is one flyer that tops them all...Braviary. The only downer is that it is a white exclusive and it evolves at level 54.
Hope this helped