#include <bits/stdc++.h>
#pragma GCC optimize("O3")
#pragma GCC target("sse4")
using namespace std;
template <class T>
bool ckmin(T& a, const T& b) {
  return b < a ? a = b, 1 : 0;
}
template <class T>
bool ckmax(T& a, const T& b) {
  return a < b ? a = b, 1 : 0;
}
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int MOD = 1000000007;
const char nl = '\n';
const int MX = 100001;
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int T;
  cin >> T;
  while (T--) {
    int N;
    cin >> N;
    vector<int> A(N);
    for (int i = 0; i < (N); i++) cin >> A[i];
    int X = *max_element(A.begin(), A.end());
    for (int i = 0; i < (N); i++) {
      if (A[i] == X &&
          ((i != 0 && A[i - 1] != X) || (i != N - 1 && A[i + 1] != X))) {
        cout << i + 1 << nl;
        goto done;
      }
    }
    cout << -1 << nl;
  done:;
  }
  return 0;
}
