I would use Flygon as a UU sweeper, and Kingdra as an Uber rain sweeper. Flygon and Kingdra are the main dragons in UU, but I feel that Kingdra benefits more from Swift Swim, and Kyogre is in Uber. You could also use it in OU, and instead have its Sniper ability to increase the damage done on crit hits.
Item: Choice Scarf/ Band
EVs: 252 Atk, 252 Speed, 4 HP
Nature: Adamant/ Jolly
Outrage/ Dragon Claw
Rock Slide/ Stone Edge
Ability: Swift Swim
Item: Life Orb/ Sniper
EVs: 200 Speed, 252 Sp. Atk 56 HP
Draco Meteor (-2 sp. atk)/ Scald (burn hax)
Kingdra has the advantage of being able to run a physical set or a special set. Flygon mainly runs a physical set. Personally, I'd use Flygon in UU, and Kingdra in OU/ Uber. Depends which tier you want to play in and/ or what role you want them to fill. You have to think about Flygon's x4 Ice weakness too, while Kingdra has the distinction of being one of 2 dragons only weak to Dragon moves, the other of Palkia.