In my opinion, EVENT_PLAYER_ACTIVATED is the ESO equivalent of WoW's "PLAYER_ENTERING_WORLD". It fires at login and upon every load screen.
/edit: Also, EVENT_PLAYER_ACTIVATED fires after EVENT_ADDON_LOADED events fire. If you are having issues at load and want to print a debug statement to the chat frame, in my experience, EVENT_PLAYER_ACTIVATED is the event to use for this, as EVENT_ADDON_LOADED is too early for the chat frame.
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