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

'''input
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

''' 

from collections import defaultdict, deque

def solve():
	n = int(input())
	a = list(map(int, input().split()))
	m = max(a)
	for i in a:
		if i!=m:
			break
	else:
		print(-1)
		return None
	for i in range(1, n-1):
		if a[i] == m and (a[i+1]!=m or a[i-1]!=m):
			print(i+1)
			return None
	if a[0] == m and a[1]!=m:
		print(1)
	else:
		print(n)

def main():
	t = 1
	t = int(input())
	for _ in range(t):
		solve()
main()