#include <bits/stdc++.h>
#pragma GCC optimize("Ofast")
using namespace std;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> v(n);
    for (int& i : v) cin >> i;
    int m = v[0];
    int mind = 0;
    for (int i = 1; i < n - 1; i++) {
      if (v[i] > v[i - 1] || v[i] > v[i + 1]) {
        if (v[i] >= m) {
          m = v[i];
          mind = i;
        }
      }
    }
    if (v[n - 1] >= m && v[n - 1] > v[n - 2]) {
      mind = n - 1;
    }
    int flag = 0;
    for (int i = 0; i < n - 1; i++) {
      if (v[i] != v[i + 1]) {
        flag++;
        break;
      }
    }
    if (flag == 0) {
      cout << "-1\n";
    } else {
      cout << mind + 1 << "\n";
    }
  }
}
