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;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    vector<long long> v;
    map<long long, long long> m;
    long long x;
    for (long long i = 1; i <= n; i++) {
      cin >> x;
      v.push_back(x);
      m[x]++;
    }
    if (m.size() == 1)
      cout << -1 << endl;
    else {
      long long Max = *max_element(v.begin(), v.end());
      for (long long i = 0; i < n; i++) {
        if (i == 0 and v[i] > v[i + 1] and v[i] == Max) {
          cout << i + 1 << endl;
          break;
        } else if (i == n - 1 and v[i] > v[i - 1] and v[i] == Max)
          cout << i + 1 << endl;
        else if (v[i] == Max and (v[i] > v[i - 1] or v[i] > v[i + 1])) {
          cout << i + 1 << endl;
          break;
        }
      }
    }
  }
  return 0;
}
