#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int Tests;
  cin >> Tests;
  for (int Test = 1; Test <= Tests; ++Test) {
    int n, ok = -1;
    cin >> n;
    int arr[n + 2];
    for (int i = 1; i <= n; ++i) cin >> arr[i];
    int mx = *max_element(arr + 1, arr + n + 1);
    arr[0] = arr[n + 1] = mx;
    for (int i = 1; i <= n; ++i)
      if (arr[i] == mx)
        if (arr[i - 1] != arr[i] || arr[i + 1] != arr[i]) {
          ok = i;
          break;
        }
    cout << ok << '\n';
  }
  return 0;
}
