#include <bits/stdc++.h>
using namespace std;
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> v(n);
    vector<int> p(n);
    for (int i = 0; i < n; i++) {
      cin >> v[i];
      p[i] = v[i];
    }
    sort(v.begin(), v.end());
    if (v[0] == v.back()) {
      cout << -1 << '\n';
      continue;
    }
    int mx = *max_element(p.begin(), p.end());
    if (p[0] == mx and p[1] != mx)
      cout << 1 << '\n';
    else if (p[n - 1] == mx and p[n - 2] != mx)
      cout << n << '\n';
    else
      for (int i = 1; i < n - 1; i++) {
        if (p[i] == mx and (p[i - 1] != mx or p[i + 1] != mx)) {
          cout << i + 1 << '\n';
          break;
        }
      }
  }
  return 0;
}
