#include <bits/stdc++.h>
using namespace std;
int main() {
  long long t;
  cin >> t;
  while (t--) {
    long long n;
    cin >> n;
    long long a[n], max_val = -1;
    for (long long i = 0; i < n; i++) {
      cin >> a[i];
      max_val = max(max_val, a[i]);
    }
    long long ans = -1;
    for (long long i = 0; i < n; i++) {
      if (max_val == a[i])
        if ((i > 0 && a[i] > a[i - 1]) || (i < n - 1 && a[i] > a[i + 1]))
          ans = i + 1;
    }
    cout << ans << endl;
  }
  return 0;
}
