Atra du evarinya ono varda.
Eelektross for SURE. This electric eel got no weaknesses yo. It's like all chill, like, imma electric-type yet no ground-type move can hit me cuz I can levitate yo.
Really. Eelektross has access to Flamethrower. An electric-type with a fire-type move: now that's gotta rock. It has access to either Coil/Acid Spray depending on which moveset you're aiming for - Coil for Physical or Acid Spray for Special. Get hit by any of those moves followed by Wild Charge/Thunderbolt and the opposing Pokemon'll go down fo' sure.
I've used Eelektross in all my teams and it has never failed me. Sorry Klang, but the electric eel wins my vote.
Excuse the writing style; I'm sleepy at the time of writing this so I'm feeling a little loopy lolol.