#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    int arr[n];
    int max = 0;
    bool flag = false;
    for (int i = 0; i < n; i++) {
      cin >> arr[i];
      if (arr[max] <= arr[i]) max = i;
      if (i >= 1) {
        if (arr[i] != arr[i - 1]) flag = true;
      }
    }
    if (!flag)
      cout << -1;
    else {
      int ans = max;
      for (int i = 1; i < n - 1; i++) {
        if ((arr[i] == arr[max]) &&
            ((arr[i - 1] < arr[max]) || (arr[i + 1] < arr[max]))) {
          ans = i;
          break;
        }
      }
      cout << ans + 1;
    }
    cout << endl;
  }
}
