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

import string

loopnumber = int(input())

while loopnumber > 0:
	piranas = int(input())
	a = list(map(int, input().split()))
	m = 0
	flag = 0
	temp = a[0]
	for i in range(0,piranas):
		if a[i] != temp:
			flag = 1
		if a[i] > m:
			if i == 0:
				if a[1] < a[0]:
				 	m = a[i]
				 	index = i
			elif i == piranas-1:
				if a[piranas-2] < a[piranas-1]:
					m = [i]
					index = i
			elif a[i-1] < a[i] or a[i+1] < a[i]:
				m = a[i]
				index = i
	if flag == 1:
		print(index+1)
	else:
		print("-1")
	loopnumber -= 1


