#include <bits/stdc++.h>
using namespace std;
const double epsilon = 1e-7;
void solve() {
  int n;
  cin >> n;
  vector<int> v(n);
  for (int i = 0; i < n; ++i) cin >> v[i];
  int res = -1;
  int mx = *max_element(v.begin(), v.end());
  for (int i = 0; i < n; ++i) {
    if (v[i] != mx) continue;
    if (i and v[i - 1] != mx) {
      res = i + 1;
      break;
    }
    if (i < n - 1 and v[i + 1] != mx) {
      res = i + 1;
      break;
    }
  }
  cout << res << endl;
}
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int t;
  cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}
