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

for i in range(int(input())):
	n = int(input())
	lst = list(map(int, input().split()))
	mx = max(lst)
	mn = min(lst)
	if(mx == mn):
		print(-1)
	else:
		idx = -1
		if lst[0] == mx and lst[1] != mx:
			idx = 0
			print(idx + 1)
			continue
		else:
			for j in range(1, len(lst) - 1):
				if lst[j] == mx and (lst[j + 1] != mx or lst[j - 1] != mx):
					idx = j
					break
			else:
				idx = len(lst) - 1
			print(idx + 1)