1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n;
  cin >> n;
  vector<int> arr(n, 0);
  set<int> s;
  for (int i = 0; i < n; i++) {
    cin >> arr[i];
    s.insert(arr[i]);
  }
  if (s.size() == 1) {
    cout << -1 << endl;
    return;
  }
  int mx = 0;
  int midx = -1;
  for (int i = 0; i < n; i++) {
    if (arr[i] >= mx) {
      mx = arr[i];
      bool cond = false;
      if (i > 0 && arr[i] > arr[i - 1]) cond = true;
      if (i < n - 1 && arr[i] > arr[i + 1]) cond = true;
      if (cond) {
        midx = i + 1;
      }
    }
  }
  cout << midx << endl;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  int T;
  T = 1;
  cin >> T;
  while (T--) {
    solve();
  }
  return 0;
}
