Out of the two (Garchomp and Kingdra), the only pokemon that can lay 'traps' is Garchomp, which can lay stealth rock. However, Tyranitar might be more suited to do that, since it is often regarded as more of a lead pokemon, and in which Garchomp is more suited for sweeping. Or, if you're running a lead Metagross, it can lay stealth rock for you.
As for type coverage, it depends on what moves you give Kingdra or Garchomp.
Kingdra's usual set is the Sub + Dragon Dance set:
~ Dragon Dance
Which you'd only get the typing coverage by Water and Dragon (against Fire, Rock, Ground, and Dragon). Then again, you can also run a special set with Hidden Power Electric against opposing Water types, or Flying types.
Garchomp's SD set:
~ Swords Dance
~ Outrage / Dragon Claw
~ Fire Fang / Aqua Tail / Stone Edge
Can give you move coverage than Kingdra, depending on your preference (against Dragon, Fire, Rock, Electric, Grass, Bug, Flying, Ice).