I think Dragon Dance Kingdra is better than Specs Kingdra. It doesn't rely on Rain to be able to sweep. And you equip it with Lum Berry to stop Thunder Wave, Toxic and Scald Burns.
I've had great success with this set:
@ Lum Berry
Swift Swim
Adamant nature
36 HP / 252 Atk / 220 Spe
~ Dragon Dance
~ Outrage
~ Waterfall
~ Disable
Switch into one of Kingdra's many resistances and then Dragon Dance up. Depending on what your opponent does next, you have all the answers. If they hit you with their best attack and go for the 2HKO, you simply use Disable next turn and remove that move from their arsenal, rendering them helpless. Disable will usually go first after the speed boost from Dragon Dance (and Swift Swift is your opponent is unlucky enough to be running a rain team). Then you can choose to Dragon Dance again to boost your Attack and Speed further, or you can begin the carnage and start spamming Outrage or Waterfall. Even counters like Ferrothorn and Jirachi die to this set. They can be 2HKO'd by either move after you have Dragon Danced twice, and Waterfall's flinch effect also helps. And if need be you can Disable their Power Whip or Body Slam, rendering them powerless.
To counter a Kingdra Sweep your opponent will throw Sleep, Burn and Paralysis at you, but Lum Berry makes that strategy null and void. And Lum Berry also works wonders when Outrage finishes and you're saved from confusion.
It's not unbeatable, but so far the results from testing this set have been amazing and it shows Disable is really underrated as a move (100% accuracy, disables for 4-7 turns). It functions similar to Substitute in other mentioned sets, but this is more permanent and doesn't drain your HP.