#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  ;
  long long t, tt;
  cin >> tt;
  for (t = 1; t <= tt; t++) {
    int n;
    cin >> n;
    int a[n], c = 1;
    for (int i = 0; i < n; i++) {
      cin >> a[i];
      if (a[i] == a[i - 1] and i > 0) c++;
    }
    if (c == n) {
      cout << -1 << '\n';
      continue;
    }
    int hi = 0, ans;
    for (int i = 0; i < n; i++) {
      if (a[i] > hi &&
          ((i > 0 and a[i] > a[i - 1]) || (i < n - 1 and a[i] > a[i + 1]))) {
        hi = a[i];
        ans = i;
      }
    }
    cout << ans + 1 << '\n';
  }
}
