#include <bits/stdc++.h>
using namespace std;
signed main() {
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    vector<long long> v(n);
    for (long long i = 0; i < n; i++) {
      cin >> v[i];
    }
    set<long long> s;
    for (long long i = 0; i < n; i++) {
      s.insert(v[i]);
    }
    if (s.size() == 1) {
      cout << -1 << endl;
    } else {
      auto it = s.end();
      --it;
      for (long long i = 0; i < n; i++) {
        if (*it == v[i]) {
          if (i - 1 >= 0 && v[i - 1] != *it) {
            cout << i + 1 << endl;
            break;
          }
          if (i + 1 < n && v[i + 1] != *it) {
            cout << i + 1 << endl;
            break;
          }
        }
      }
    }
  }
  return 0;
}
