I gotta go with Gen I on this one. Nidoking, Tentacruel, Gengar, Victreebel, and Venomoth are all pretty good. They just have the sheer numbers, and unlike Normal, the numbers are actually of a high quality.
VIII gets second place, with Toxtricity, Overqwil, and G-Slowking as the driving force.
Not sure about third, but I'm leaning IV for Roserade and Toxicroak. Maybe VII.