The event-driven method is more efficient because your code reacts instantly when the ESP disconnects, instead of waiting for a timer to notice the problem. For example, on the ESP32 you can use:

#include <WiFi.h>

void WiFiEvent(WiFiEvent_t event) {
  switch (event) {
    case SYSTEM_EVENT_STA_DISCONNECTED:
      Serial.println("WiFi disconnected! Reconnecting...");
      WiFi.reconnect();
      break;
    case SYSTEM_EVENT_STA_CONNECTED:
      Serial.println("WiFi connected!");
      break;
  }
}

void setup() {
  Serial.begin(115200);
  WiFi.onEvent(WiFiEvent);
  WiFi.begin("YourSSID", "YourPassword");
}

void loop() {
  // Your main code
}

With this setup, the ESP automatically attempts to reconnect whenever the connection drops, without wasting resources on continuous polling.