#include <bits/stdc++.h>
using namespace std;
long long bin_pow(long long a, long long b) {
  if (b == 0) return 1;
  if (b % 2 == 0) {
    long long t = bin_pow(a, b / 2);
    return t * t % 1000000007;
  } else
    return a * bin_pow(a, b - 1) % 1000000007;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  long long t = 1, n, m, k = 0, sum = 0, l = 0, r = 0, x = 0, y = 0, z = 0,
            ans = 0, mn = LLONG_MAX, mx = LLONG_MIN;
  cin >> t;
  while (t--) {
    ans = z = 0;
    cin >> n;
    vector<long long> a(n);
    set<long long> s;
    for (int i = 0; i < n; i++) cin >> a[i], s.insert(a[i]);
    if (s.size() == 1)
      ans = -1;
    else {
      for (int i = 0; i < n; i++) {
        if (a[i] > z) {
          z = a[i];
        }
      }
      for (int i = 0; i < n; i++) {
        if (a[i] == z) {
          if ((i > 0 && a[i - 1] < a[i]) || (i < n - 1 && a[i + 1] < a[i])) {
            ans = i + 1;
            break;
          }
        }
      }
    }
    cout << ans;
    cout << "\n";
  }
  return 0;
}
