#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  long long int t;
  cin >> t;
  while (t--) {
    long long int n, i, j, k, m, x, y, flag = 0;
    cin >> n;
    vector<long long int> a(n);
    long long int mx = 0;
    for (int i = 0; i < n; i++) {
      cin >> a[i];
      mx = max(mx, a[i]);
    }
    x = a[0];
    for (int i = 0; i < n; i++) {
      if (a[i] == x) flag++;
    }
    if (flag == n)
      cout << "-1\n";
    else {
      for (int i = 0; i < n; i++) {
        if (i < n - 1 && a[i] == mx && a[i + 1] < mx) {
          cout << i + 1 << endl;
          flag = -1;
          break;
        }
        if (i > 0 && a[i] == mx && a[i - 1] < mx) {
          cout << i + 1 << endl;
          flag = -1;
          break;
        }
      }
      if (flag == -1) continue;
    }
  }
  return 0;
}
