Storm is the most obvious choice. Between Gale, Freezing Rain, Tornado, and Lightning Storm the mobs are liable to forget they even have legs. For a Controller, you can pair with Fire (Bonfire), Earth (Earthquake), or Ice (Ice Slick) for even more KD. Personally, I find Fire/Storm to be one of the most enjoyable Controller combos, but Earth/Storm has a bit more synergy. On Corruptors and Defenders, Water and Energy will give you KB/KD as well.
Blasters get Bonfire in their APP, so you can pair that with Energy or Water for lots of KD. For secondaries, Earth (Tremor) and Electric (Thunder Strike, Force of Thunder) give you even more options.
Melee can work too. Shield Defense for Shield Charge. For offense Electric Melee can utilize Thunder Strike, Lightning Clap (non-Stalker), and Lightning Rod. Ice Melee has Ice Patch, which is easily permanent and keeps foes down quite easily. There's also Super Strength with KD on most of its attacks (most notably Foot Stomp), plus Hand Clap for fun. Stone Melee, Titan Weapons, and War Mace get a lot of KD too, though TW cannot pair with Shield.