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;
  int a[n];
  int maxi = 0, cnt = 0, ind = -1;
  for (int i = 0; i < n; ++i) {
    cin >> a[i];
    if (a[i] > maxi) {
      ind = i + 1;
      maxi = a[i];
      cnt = 1;
    } else if (a[i] == maxi) {
      if (i != n - 1) ind = i + 1;
      cnt++;
    }
  }
  if (cnt == n)
    cout << -1 << "\n";
  else
    cout << ind << "\n";
}
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t = 1;
  cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}
