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


t = int(input())
for _ in range(t):
	n = int(input())
	arr = list(map(int, input().split(' ')))
	if max(arr) == min(arr):
		print(-1)
	else:
		largest = max(arr)
		smallest = min(arr)
		i = 0
		while i < n:
			if arr[i] == largest and i == 0 and arr[i] > arr[i +1]:
				print(i +1)
				break
			elif arr[i] == largest and i == n -1 and arr[i] > arr[i -1]:
				print(i +1)
				break
			elif i != 0 and i != n -1 and arr[i] == largest and (arr[i] > arr[i -1] or arr[i] > arr[i +1]):
				print(i +1)
				break
			i += 1

