Poison types are weak against Ground and Psychic types.
Poison Type moves are super effective against only Grass Types.
Fairy-type Pokemon are weak against Steel and Poison-type attacks.
no
Grass-type Pokemon are weak against Fire, Flying, Poison, Ice, and Bug-type attacks.
Poison types are weak against Ground and Psychic types.
they r weak against fire, flying, poison, bug and ice
Poison Type moves are super effective against only Grass Types.
Poison is strong against Grass. It's weak against Poison, Ground, Rock, and Ghost. It can't affect Steel. Ground and Psychic are strong against Poison. Grass, Fighting, Poison, and Bug are weak against Poison.
Fairy-type Pokemon are weak against Steel and Poison-type attacks.
Electric, Fire, Poison, Rock, Steel
I assume that you are referring to Fighting-Type Pokémon. When attacking, they are weak against Poison-Types, Flying-Types, Bug-Types, and Psychic-Types, and ineffective against Ghost-Types. When defending, they are weak against Flying-Types and Psychic-Types.
Tentacool/Tentacruel are Water/Poison-type Pokemon, so they are weak against Psychic, Electric, and Ground-type attacks.
Grass-type Pokemon are weak against Fire, Flying, Poison, Ice, and Bug-type attacks.
no
Gardevoir is weak against the Ghost, Poison and Steel-types.
I would say poison type, as normal type moves are not very effective, neither are fire attacks, and bug types are weak against rock. Therefore, I conclude that poison type, depending on your pokémon's attacks, you should go with your poison type pokémon.