It actually depends on what you are using for them(special or physical)
Hydreigon
Pros:
- nice special attack at 125
- Decent bulk @92/90/90
- Pretty diverse movepool with great moves and coverage
- Levitate is a decent ability
- Special: Draco meteor, dragon pulse, flamethrower/fire blast, dark pulse, flash cannon, hydro pump/surf/tri attack/nasty plot
Choice specs with Draco meteor can do a lot of damage
I advise again at physical as its higher attack stat is physical but if you want
https://pokemondb.net/pokebase/13040/what-is-a-good-moveset-for-hydreigon?show=13044#a13044
Cons:
- hard for it to ko fairies with flash cannon without a nasty plot or choice specs boost.
- a fairy move normally spells certain death.
- typing in a way debuffs it as it get hit bad by common moves like you turn and any fighting attack.
-98 spe is decent but still is a bit slow.
Dragapult
Conflict between special or physical
Pros:
- Excellent speed@base 142
- powerful and fast sweeper with 120 atk/100sp.atk
- very diverse special movepool - similar to hydreigon's
- nice abilities with clear body - blocking intimidate (if physical) and sticky web.
Infiltrator going pass sub and others
Cons:
- slight low defenses@88/75/75
- shallow physical movepool
For move set:
https://pokemondb.net/pokebase/330850/what-is-a-good-moveset-for-dragapult
