1
3
5 3 4
 6
5
5 3 4 4 5
3
1 1 1
5
4 4 3 4 4
5
5 5 4 3 2
3
1 1 2
5
5 4 3 5 5
 1
3
10 1 5

1
 1
-1
2
2
3
1
 1

#include <bits/stdc++.h>
using namespace std;
long long power(long long x, long long y);
long long mpower(long long x, long long y, long long p);
long long modInv(long long a, long long m);
long long gcdExtended(long long a, long long b, long long *x, long long *y);
bool isPrime(long long n);
void solve() {
  long long n, mx = -1, cnt = 0, i;
  cin >> n;
  long long ar[n];
  for (i = 0; i < n; i++) {
    cin >> ar[i];
    if (i > 0 && ar[i] == ar[0]) cnt++;
    mx = max(mx, ar[i]);
  }
  for (i = 0; i < n; i++) {
    if (ar[i] == mx) {
      if (i > 0 && i < n - 1) {
        if (ar[i - 1] != ar[i] || ar[i + 1] != ar[i]) break;
      } else if (i == 0 && ar[1] != ar[0])
        break;
      else if (i == n - 1 && ar[n - 2] != ar[n - 1])
        break;
    }
  }
  if (cnt == n - 1)
    cout << -1;
  else
    cout << i + 1;
  cout << "\n";
  return;
}
signed main() {
  ios_base::sync_with_stdio(false), cin.tie(0), cout.tie(0);
  srand(time(NULL));
  long long t = 1;
  cin >> t;
  while (t--) solve();
}
long long modInv(long long a, long long m) {
  long long x, y;
  long long g = gcdExtended(a, m, &x, &y);
  long long res = (x % m + m) % m;
  return res;
}
long long gcdExtended(long long a, long long b, long long *x, long long *y) {
  if (a == 0) {
    *x = 0, *y = 1;
    return b;
  }
  long long x1, y1;
  long long gcd = gcdExtended(b % a, a, &x1, &y1);
  *x = y1 - (b / a) * x1;
  *y = x1;
  return gcd;
}
long long mpower(long long x, long long y, long long p) {
  long long res = 1;
  x = x % p;
  while (y > 0) {
    if (y & 1) res = (res * x) % p;
    y = y >> 1;
    x = (x * x) % p;
  }
  return res;
}
long long power(long long x, long long y) {
  long long res = 1;
  while (y > 0) {
    if (y & 1) res = res * x;
    y = y >> 1;
    x = x * x;
  }
  return res;
}
bool isPrime(long long n) {
  if (n <= 1) return false;
  if (n <= 3) return true;
  if (n % 2 == 0 || n % 3 == 0) return false;
  long long p = sqrt(n);
  for (int i = 5; i <= p; i = i + 6)
    if (n % i == 0 || n % (i + 2) == 0) return false;
  return true;
}
