In 2019-2021, Pokemon. But Animal Crossing, I predict, will win in the end. Why?
Pokemon usually launches multiple generations in each console generation. Also, with a multitude of spinoffs, Let's Go, and other games they will cannabalize. Will Pokemon as a brand sell more than Animal Crossing as a brand on Switch? No doubt. But there is only ever one main Animal Crossing per hardware generation (if that). New Leaf blew the door open on this series potential sales wise, and I think it is just getting started.
All this is if they give us a traditional AC experience. If they go the always online town route, where you live with computers and other gamers in real time online, then AC is going to be far higher in sales than New Leaf.