#include <bits/stdc++.h>
using namespace std;
int t, n, maxi, maxx, a[300005], ans;
int main() {
  scanf("%d", &t);
  while (t--) {
    scanf("%d", &n);
    maxx = 0, maxi = -1;
    for (int i = 1; i <= n; i++) {
      scanf("%d", &a[i]);
      if (a[i] >= maxx) maxx = a[i];
    }
    for (int i = 1; i <= n; i++) {
      if (a[i] == maxx) {
        if (i > 1 && a[i] > a[i - 1]) {
          maxi = i;
          break;
        }
        if (i < n && a[i] > a[i + 1]) {
          maxi = i;
          break;
        }
      }
    }
    printf("%d\n", maxi);
  }
  return 0;
}
