The top champs globally to counter Zeri include Elise, Naafiri, and Volibear. These champions are all great at countering Zeri with high win rates over 59%. Even if these Zeri counter picks are not used in the same position as you, it's not smart to choose them into these matchups. They will often crush Zeri.
Yet, if the other team choses either Rumble or Kassadin, Zeri mains should seriously consider selecting them, as they easily dominates these champs with win rates over 55% against both ofthem.