Braedan Bruce Asked: Who Should Be My Last Pokemon?

there are many opttions for my last pokemon for my heartgold team adn i need your help picking
Gengar=Shadow Ball, Sludge Bomb, Hypnosis, Dream Eater
Nidoking=Earthpower, Sludge Bomb, Mega Horn, Shadow Ball
Espeon=Psychic, Shadow Ball, Morinig Sun, Sand-attack
Arbok=Gunk Shot, Ice Fang, Sludge Bomb, Earthquake
Muk=Gunk Shot, Mud bomb, Sludge Bomb, Shadow Ball

and the rest of my team is

Dragonite=Draco Meteor, Fire Punch, Outrage, Wing attack
Empoleon=Surf, Ice Beam, Flash Cannon, Drill Peck
Venusaur=Earthquake, Sunny Day, Poison Powder, Solar Bam
Charizard=Fly, Flamethrower, Dragon Claw, Flare Blitz
Raikou=Thunderbolt, Substitute, Thunder Fang, Iron Tail

so help me pick
im leaining towards gengar or nidoking