Israeli and various Eastern European nationalisms are the most entrenched socially and politically in their countries, but something like Japanese nationalism or Hindu nationalism might be "most potent" overall due to those countries being stronger geopolitical actors.
I was also thinking along the lines of it being a powerful and exclusive third rail in domestic politics. Jewish nationalism in Israel, for example, is pretty broadly embraced by all parties except a few of the Arab groups. The parties differ in their interpretation of what a "nation for the Jewish people" is, but they all claim some part of a shared national heritage.
Hindu nationalism, on the other hand, is an active and explosive political movement on the march in India. I agree that Japanese nationalism also fits this understanding well.
