#include <bits/stdc++.h>
using namespace std;
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    vector<long long> a(n);
    set<long long> st;
    long long mx = -1;
    for (long long i = 0; i < n; i++) {
      cin >> a[i];
      if (mx < a[i]) {
        mx = a[i];
      }
      st.insert(a[i]);
    }
    if (st.size() == 1) {
      cout << -1 << endl;
    } else {
      bool ok = false;
      for (long long i = 0; i < n; i++) {
        if (a[i] == mx &&
            ((i != n - 1 && a[i + 1] < a[i]) || (i != 0 && a[i - 1] < a[i]))) {
          cout << i + 1 << endl;
          break;
        }
      }
    }
  }
  return 0;
}
