Anti venom, he's more versatile. Viv can't really punch up too much and once she finishes her rotation, its a real pain to begin it again. So she only has a certain amount of reach.
Anti-Venom. Versatile utility and massive damage. Viv has these as well but she has a fairly strict loop and once that loop is done, it take awhile before you can do again. With Anti-Venom you build up to an SP2 an you can keep the damage not just rolling but also escalating if the opponent has a bunch of health. I don't know many champs that can get 7-10x+ their base attack and maintain it. Then if you mess up, with his awakened ability you can regen back some lost health. His utility is pretty amazing, counters unstoppable, evade, reduce/ reverse powergain and healing, up to 75% reduction in defensive ability accuracy, a science champ that can stagger, block mystic unblockable attacks, and he is poison/ incinerate immune.
I like Viv but she has a strict loop and kinda unforgiving playstyle.