#include <bits/stdc++.h>
using namespace std;
const int maxn = 3e5 + 5;
long long t, n, a[maxn];
int main() {
  scanf("%d", &t);
  while (t--) {
    long long maxx = -1e18, ans = 0;
    cin >> n;
    for (int i = 0; i < n; i++) {
      cin >> a[i];
      if (a[i] > maxx) maxx = a[i];
    }
    for (int i = 0; i < n; i++) {
      if (maxx == a[i]) {
        if (i == 0 && a[0] > a[1]) {
          ans = 1;
          break;
        } else if (i == n - 1 && a[n - 1] > a[n - 2]) {
          ans = n;
          break;
        } else if (((i != 0) && a[i] > a[i - 1]) ||
                   (i != n - 1 && a[i] > a[i + 1])) {
          ans = i + 1;
          break;
        }
      }
    }
    if (ans == 0)
      cout << -1 << endl;
    else
      cout << ans << endl;
  }
  return 0;
}
