Which Pokémon Game is Best for a Mono-Type Poison Team?

Once the most populace Pokémon type, Poison has been a bit ignored as of late as far as NEW Pokémon being added. However that doesn't mean that all of the newer games are bad to use Poison types if you feel so inclined to use some of the most corrosive and venomous Pokémon around! So let's see which region might be the best for embracing entropy and using a team made entirely of Poison types...