There both good in pvp but it depends if you're a shotgun person or a hand cannon people. If you run fusion rifles over shotgun duality isnt going to suddenly change that. Its unique in the sense that it can be a slug and a pellet shotgun so if you like both those shotguns, go for it. Ace is a really good hand cannon for pvp, but if you don't use hand cannons it's not the choice for you. If you both like both shotguns and hand cannons, I'd go with ace since you can get more usage out of it since it's a primary