Hypothetical ivysaur/venusaur training question

With all these new ivysaur and venusaur I have it brought up a question for me regarding training up gyms. I would be using ivysaur etc for training against water types (usually vaporeons). My question is if I have an ivysaur with sludge bomb as my charge move is it more damage to only be using vine whip/razor leaf since it will be doing super effective damage? Or is it more damage to use the grass move in combination with sludge bomb(not super effective but STAB)?

Thanks in advance