#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    vector<int> v(n, 0);
    int maxi = 0, mini = INT_MAX;
    for (int i = 0; i < n; i++) {
      cin >> v[i];
      maxi = max(maxi, v[i]);
      mini = min(mini, v[i]);
    }
    int left = 0, right = 0;
    for (int i = 0; i < n; i++) {
      if (v[i] == maxi and left == 0) left = i + 1;
      if (v[i] == maxi) right = i + 1;
      if (left != 0 and right != 0 and v[i] != maxi) break;
    }
    if (mini == maxi)
      cout << -1 << endl;
    else {
      if (left - 1 != 0 and v[left - 2] < v[left - 1])
        cout << left << endl;
      else
        cout << right << endl;
    }
  }
}
