The greatest champs globally to counter Viktor include Zeri, Aphelios, and Kalista. These are all good at countering Viktor with decent win rates over 54%. Even if these Viktor counter picks are not used in your lane, it's not a good idea to take him into these matchups. They will most often crush Viktor.
Yet, if the opposite team choses either Amumu or Tahm Kench, you should seriously consider picking him, as he easily wins against these champs with win rates over 54% against each ofthem.