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

# -*- coding: utf-8 -*-
"""
Created on Sat Sep 19 16:36:57 2020

@author: lakne
"""
t = int(input())
answers = []
for _ in range(t):
    n = int(input())
    a = input().split()
    a = list(map(int, a))
    if a.count(a[0]) == n:
        answers.append(-1)
    else:
        big = max(a)
        if a.count(big) == 1:
            answers.append(a.index(big)+1)
        else:
            for i in range(n):
                if i == 0 and a[i] == big and a[i+1] != a[i]:
                    answers.append(i+1)
                    break
                elif i == n-1 and a[i] == big and a[i-1] != a[i]:
                    answers.append(i+1)
                    break
                elif i != 0 and i != n-1 and a[i] == big and (a[i+1] != a[i] or a[i-1] != a[i]):
                    answers.append(i+1)
                    break
for j in range(t):
    print(answers[j])