#include <bits/stdc++.h>
using namespace std;
const int max1 = 3e5 + 5;
int a[max1];
signed main() {
  ios::sync_with_stdio(false);
  int t, n;
  cin >> t;
  while (t--) {
    int n, flag = 1, ans, max = 0;
    cin >> n;
    for (int i = 0; i < n; i++) {
      cin >> a[i];
      if (a[i] > max) max = a[i];
      if (i > 0 && a[i - 1] != a[i]) flag = 0;
    }
    if (flag == 1)
      cout << "-1" << '\n';
    else {
      for (int i = 0; i < n; i++) {
        if (a[i] == max) {
          if (i != 0 && a[i - 1] != max) {
            ans = i + 1;
            break;
          }
          if (i != n - 1 && a[i + 1] != max) {
            ans = i + 1;
            break;
          }
        }
      }
      cout << ans << '\n';
    }
  }
}
