#include <bits/stdc++.h>
using namespace std;
void solve() {
  int n;
  cin >> n;
  std::vector<int> v;
  int maxi = 0;
  for (long long i = 0; i < n; i++) {
    int a;
    cin >> a;
    v.push_back(a);
    maxi = max(maxi, a);
  }
  int ans = -1;
  for (long long i = 0; i < n; i++) {
    if (v[i] == maxi &&
        ((v[i] > v[i + 1] && i < n - 1) || (i > 0 && v[i] > v[i - 1]))) {
      ans = i + 1;
    }
  }
  cout << ans << '\n';
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);
  int t = 1;
  cin >> t;
  while (t--) {
    solve();
  }
  return 0;
}
