#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int t = 1;
  cin >> t;
  while (t--) {
    int n, mx = -1;
    cin >> n;
    int arr[n];
    for (int i = 0; i < n; i++) {
      cin >> arr[i];
      mx = max(mx, arr[i]);
    }
    int ans = -1;
    for (int i = 1; i < n; i++)
      if (arr[i] == mx && arr[i - 1] != mx) ans = i + 1;
    for (int i = 0; i < n - 1; i++)
      if (arr[i] == mx && arr[i + 1] != mx) ans = i + 1;
    cout << ans << ("\n");
  }
  return 0;
}
